Here's what I've got, and please add your advice:
1) Dictation with repetition. What this means is that you take a segment or some audio or audio/visual content, and you listen to it / watch it over and over again with no additional textual assistance (no script, no subtitles, etc). You then write out everything that is being said, word for word as best you can. If you are unsure of something, if possible, find a native speaker to help you, otherwise skip it after 10 or so tries (and fails). Then, this is the critical part, speak audibly (out loud) what you've just transcribed. Whether it's a movie script you just made from watching your favorite movie, or the radio NHK news broadcast, speak it out loud.
First, just get a feeling for how it sounds to speak it, and get a general idea of what it is. Then, try it again, this time speaking along with or shadowing the speaker as best you can [If you don't know, shadowing means saying what the speaker is saying immediately after they say it, so you're always staying a little behind but sticking with it]. Then, do it without stopping the video / audio at all, trying to keep up as best as possible. This is a HUGELY important point: focus on comprehending what you're saying first. Then, and only then, focus more on pronunciation and more natural intonation.
Now, note patterns. For example, if you notice that ﾂ「窶堋ｵ窶堙寂?堙ｧ窶堋ｭﾂ」 is often followed with ﾂ「窶堋ｷ窶堙ｩ窶堙?」, try to memorize that particularly phrase, ﾂ「窶堋ｵ窶堙寂?堙ｧ窶堋ｭ窶堋ｷ窶堙ｩ窶堙?」. Language is not mainly a combination of individual words, but a combination of phrases. Another more grammatical example might be ﾂ「窶堋ｾ窶堋ｩ窶堙ｧﾂ」and ﾂ「ﾂ≫?凪?堋ｩ窶堙ｧﾂ」 (ﾂ≫? symbolizes the absence of 窶堋ｾ). When do you say ﾂ「窶堋ｾ窶堋ｩ窶堙ｧﾂ」and when do you say only ﾂ「窶堋ｩ窶堙ｧﾂ」? Note the patterns. For example, if you always hear ﾂ「窶堋｢窶堋｢窶堋ｩ窶堙ｧﾂ」and never ﾂ「窶堋｢窶堋｢窶堋ｾ窶堋ｩ窶堙ｧﾂ」, ask yourself why, and then look it up in a grammar book or on a website. Learn the rules firsthand this way, and then reinforce them with grammar explanations (try to find explanations in all Japanese for best results).
One more example of a different type. I often read ﾂ「ﾂ〜窶堙ｦ窶堋､窶堋ｾﾂ」 or ﾂ「ﾂ〜窶堙ｦ窶堋､窶堙??堋ｷﾂ」in textbooks and other written material, but I noticed something: I hardly ever hear anyone say it. In fact, I listened for a week, and after spending over 30-40 hours interacting with native speakers, I never heard it once except in a sermon (and that only once). I concluded that it must not be used in spoken language much, and is mainly used for written language or for formal speeches/events. I looked it up in a Japanese grammar book, and there it said:
ﾂ「窶堙ｦ窶堋､窶堋ｾﾂ」窶堙債鞘?倪?堋ｫﾅ陳ｾ窶杯窶堙｢窶ｰﾃｼ窶堙懌?堙≫?堋ｽﾋ彙窶堋ｵﾅ陳ｾ窶杯窶堙?ｽg窶堙ｭ窶堙ｪ窶堙ｩ
It sticks so much better in my mind when I discover it in realistic communication versus merely reading about it in a grammar book. At the same time, without the grammar book, I wouldn't have that reassuring professional opinion to refer to.
2) Find good language material and mimic it over and over. Only repeating a dialog once will not solidify it in the mind. And, it's been nearly proven that we now realize that muscle seems to have a "memory" (not inside the muscle, but how the brain categorizes information and uses seems to indicate that muscle develops memory from habitual repetition). People who clench their teeth tend to do so without realizing it, and people who train in martial arts or even a sport like baseball seem to just "know" instantly how to move to achieve the desired result. Likewise, you must train your mouth and tongue to move exactly how they should for different phrases. If we don't do this, we constantly stumble over our words and we become nearly incomprehensible to our listeners.
By "good language material," I have two definitions. The first is obvious: find material that has realistic, natural language that native speakers use in the appropriate situation. That means, don't keep training on self-made dialogs unless you're absolutely sure they are completely natural, otherwise you'll internalize errors or awkward (though grammatically correct) language. Don't train yourself to speak in all 窶堙??堋ｷﾂ・窶堙懌?堋ｷ form if you want to speak with your similarly aged friends naturally.
The second meaning is less obvious but will become so when I say it: mimic only the material that makes you who you want to be. If you download a radio podcast designed for young listeners, and you are female and are copying a female speaker, you're pretty good to go. If you're male and copying a female, you should either know the pitfalls extremely well or find a male speaker. Furthermore, do you want to sound like a cutesy female? If so, then you can find cutesy speakers. If not, avoid girls who speak cutesy. Me personally, I have just started the hunt for male speakers who sound pretty intelligent when they speak, use occasionally big words, but yet don't sound too terribly dry. I found one guy I definitely like on the radio, and recorded some of his conversations and will be mimicking them after I transcribe it. I don't want to completely lose who I am to learn to speak Japanese.
Also, take care with dialects. Copy them if you want, but remember that someone who can only speak a non-standard dialect of a language will face unique limitations in terms of employment and social standing (the same is true of native speakers themselves).
3) Take extreme care with textbook dialogs. They are designed just for people like you, studying Japanese as a foreign language. They often contain simplified, unnecessarily polite or formal language. For example, quickly glancing through my intermediate Japanese textbook that is still lying around, I found a variety of stereotypical, less than completely natural conversations in the dialogs. I work in an office, and the average worker who decides to chat will do so in their own natural language as a friend does with a friend, dispensing with most 窶堙??堋ｷﾂ・窶堙懌?堋ｷ endings and using the common slang and dialect; that of course instantly changes if the boss comes around.
As the conversations get better (more natural language), they still have a huge, fatal flaw: every single one pretty much centers around college, studying abroad, talking to professors, etc. The only ones that branch out cover stereotypical restaurant / doctor conversations. There are no trips to the game center, no one is chatting in a car on the way to a restaurant, there are no conversations about funny things people did the day before, etc. These kinds of conversations comprise the majority of what is spoken around me outside of work with my friends. I'm being prepped for conversations I already learned how to have and don't want to have anymore. I just don't want to recycle the same old static, boring, stereotypical conversations about sushi, Kanji, how hot it is in the summer, and narrow roads and small apartments.
I haven't found a decent textbook that is more down to earth about the dialogs; they mostly center around stereotypical experiences that foreigners are supposed to have in Japan, even though I've never received a gift from my neighbors who have moved in and out, and I really don't want to talk anymore about my home country compared to Japan. If you know of one, please, by all means, PM me or post it here.
4) Reading out loud. This has been helpful for me, and it taught me many helpful phrases. Find books with lots of dialog, and read the dialog out loud many times.
5) Acting out dialogs that I have in my head is often times helpful. If I know I'm going to have a conversation about something with someone, I have it in my head beforehand. What helps me even more is if I say it out loud. I can't anticipate all the responses, so I just mostly talk from my perspective saying all the things I want to say, and whatever I am asked, I am usually prepared to give at least a basic answer. For example, when I talked to my friends about how I felt when Japanese people constantly feel the need to excessively use phrases like ﾂ「ﾆ探ﾆ停?愴鱈ﾆ停?ｦﾆ脱ﾂ」(thank you), ﾂ「ﾆ丹ﾆ鍛ﾆ檀ﾂ」(good), and ﾂ「ﾆ地ﾆ陳哉脱ﾂ」(hello), I rehearsed it first out loud by myself. I looked up how to say phrases similar to "it makes me feel" and "their intention is." I could communicate how I felt, sympathize with why they do it, and communicate what I wanted. I did not unnecessarily offend anyone, and clearly got my point across: I know why you do it, but it's unnecessarily because it sometimes makes me feel like an outcast because it singles me out as different.
6) Listening to other people talk, and paying close attention to phrases that I think would be useful for me. I try to internalize them, and as soon as possible write them down and then I can study them.
7) Swapping words in natural conversations. Find a natural conversation on radio, TV, the internet, or from memory of one in person (better have a good memory). Once you know it inside and out, start swapping words. If the person says, ﾂ「ﾅｽﾃ絶?ｰﾃｯ窶廬窶堙鞍停?ｹﾂーﾆ停?ｹ窶堋ｪ窶堋?窶堙≫?堙??堙?ﾂ、窶挧窶堙ｪ窶堙ｩ窶堙≫?堙??堋ｦ窶堋ｦ窶堙ｱ窶堋ｿ窶堙｡窶堋､ﾂ？ﾂ」. Try swapping in ﾂ「ﾅｽﾃ絶?ｰﾃｯ窶廬窶堙鞍停?ｹﾂーﾆ停?ｹ窶堋ｪ窶堋?窶堙≫?堋ｽ窶堙ｧﾂ、窶挧窶堙ｪ窶堙ｩ窶堙≫?堙??堋ｾ窶堙溪?堋ｶ窶堙｡窶堙遺?堋｢ﾂ？ﾂ」. Notice the necessary change in the verb that I had to make to follow up with my statement (two opposing opinions).
An easier way to do is simply to change the verb if possible or to change a noun. ﾂ「ﾅ?Oﾂ食窶堙娯?堙吮?堋､窶堋ｪ窶ｹCﾅ?yﾂ」can have a lot of stuff in place of ﾂ「ﾅ?Oﾂ食ﾂ」. You can also change the ﾂ「窶ｹCﾅ?yﾂ」 to something like ﾂ「ﾂ坂?壺?堋｢ﾂ」 or ﾂ「ﾂ好窶堋ｫﾂ」or ﾂ「ﾅ?y窶堋ｵ窶堋｢ﾂ」.
8) Pay special attention to natural conversation styles that non-native speakers rarely use or avoid. For example, conversation softeners like ﾂ「窶堙?ｽv窶堋､ﾂ」ﾂ・窶堋ｩ窶堙遺?塲ｸﾂ・窶堋ｩ窶堙?窶堋ｵ窶堙ｪ窶堙遺?堋｢ﾂ・窶堋ｯ窶堙?・窶堙??堋ｩﾂ・窶堙遺?堙?・ﾂ〜窶堋ｾ窶堙?窶堙? These types of phrases can sometimes carry little or no meaning; you don't really want to say "probably" or "I wonder," but sometimes it's necessary to soften the phrases you use. Also, eliciting responses from people in a natural way is difficult for non-native speakers, but watch for how people end their sentences (intonation) as well as words they use, such as ﾂ「窶堋｢窶堋｢窶堙ｱ窶堋ｶ窶堙｡窶堙遺?堋｢ﾂ？ﾂ」ﾂ・ﾂ「窶堙按！ﾂ」(rising intonation)ﾂ「ﾂ〜窶堙遺?堋｢窶堙個？ﾂ」ﾂ・ﾂ「窶堙銀?堋･窶堋･ﾂ」(falling intonation as the voice fades). Also, simple grammatical forms like ﾂ「ﾂ〜窶堙??堋ｵ窶堙懌?堋､ﾂ」 are easy to forget but make for a lot more natural conversation. For example, this sentence is a bit dry without the proper ending:
ﾂ「ﾅｽg窶堙ｭ窶堙遺?堋｢窶堙?、ﾅ陳ｾ窶杯窶堙娯?拿窶氾坂?堙坂?堋ｷ窶堋ｮ窶堙遺?堋ｭ窶堙遺?堙ｩﾂ」
This is much better:
ﾂ「 ﾅｽg窶堙ｭ窶堙遺?堋｢窶堙?、ﾅ陳ｾ窶杯窶堙娯?拿窶氾坂?堙坂?堋ｷ窶堋ｮ窶堙遺?堋ｭ窶堙遺?堙≫?堙??堋ｵ窶堙懌?堋､窶堙ｦ窶堙仰」or ﾂ「ﾅｽg窶堙ｭ窶堙遺?堋｢窶堙?、ﾅ陳ｾ窶杯窶堙娯?拿窶氾坂?堙坂?堋ｷ窶堋ｮ窶堙遺?堋ｭ窶堙遺?堙≫?堋ｿ窶堙｡窶堋､窶堙銀?堋･ﾂ」
9) This is perhaps the most difficult to do, not because it's hard, but because it's embarrassing and revealing: record yourself having a real or imagined dialog, and then listen to it / watch it afterwards. See how long you pause, try to notice any errors you make if you can, and listen to your intonation. Do you tend to favor using 窶堙遺?塲ｸ at the end of every single sentence? Is that the speaking style you want for yourself? Do you take a long time to think of vocabulary? Should you focus more on studying vocab, and if so, what area of vocabulary especially trips you up?
I've been forced to see myself on video several times using Japanese for college courses, and they were very eye-opening moments; I realized just how much I look for others to reassure me of my language ability. This makes some Japanese feel awkward or shy, because I keep indicating by my eyes and posture (as well as by excessive sentence ending particles) that I'm not sure about what I said and need reassurance. Many people can't give me that reassurance, so as I lose more confidence, they lose more confidence and become more shy/awkward, makes me feel like I'm really saying something totally screwy and I get more awkward, and the cycle moves forward.
10) This is important: learn how to buy yourself time naturally. This is essential for conversations, especially in a foreign language. For example, if you are not groping for words but are generally searching your brain for some fact or memory (such as a time, or a name, or a place), be natural and say something like this:
ﾂ「窶ｰﾂｽ窶堋ｾ窶堙≫?堋ｯﾂ」ﾂ「窶堙??堋ｱ窶堋ｾ窶堙≫?堋ｽ窶堙≫?堋ｯﾂ」ﾂ「窶ｰﾂｽ窶堙?陳ｾ窶堙≫?堋ｽ窶堙≫?堋ｯﾂ」
Say it clearly to yourself, looking away from the listener for a moment to emphasize this inner search. If you look straight at the person, you might imply that they should know this fact, and if it has nothing to do with them, they may think, "How should I know?" Also, the following are helpful and simple:
ﾂ「窶堋?窶堙娯?堋｣ﾂ」ﾂ「窶堋ｦ窶堋ｦ窶堙≫?堙?」ﾂ「窶堙?、ﾂ．ﾂ．ﾂ．ﾂ」ﾂ「窶堋ｶ窶堙｡ﾂ．ﾂ．ﾂ．ﾂ」
Just be careful that the ones like ﾂ「窶堙?、ﾂ」 are not completely nonsensical in the sense that you use them. For example, ﾂ「窶堙?、ﾂ．ﾂ．ﾂ．ﾂ」is generally not used before you start speaking, because it insinuates a direct connection to what was just said; essentially, it's the ﾂ〜窶堙 form of 窶堙??堋ｷ. I used it once to start something I said, and the people around me laughed, because I had connected what I was about to do (the welcome game for our church cell group) so closely with what was just said, and thus had a slightly comical quality to it (helped by the fact that I'm an international, not a native speaker).
Plus, if you use the ﾂ「窶堙≫?堋ｯﾂ」form to indicate your search for information, it helps the listener know what the heck you're doing when you start guessing at it. Check this out:
ﾅｽﾂｩ窶｢ﾂｪﾂ：ﾂ催ｰ窶愿ｺﾂ、窶堋ｽ窶堋ｱﾂ湘??堋ｫ窶ｰﾂｮ窶堋ｳ窶堙ｱ窶堙??ｰﾃｯ窶堙≫?堋ｽﾂ人ﾂ．ﾂ．ﾂ．
ﾋ彙窶堋ｵ窶佛?ﾅｽﾃｨﾂ：窶堋､窶堙ｱﾂ。
ﾅｽﾂｩ窶｢ﾂｪﾂ：ﾆ地ﾆ歎ﾂ．ﾂ．ﾂ．ﾆ地ﾆ歎ﾆ停?榿筑ﾂ？ ﾆ地ﾆ団ﾆ停?榿筑ﾂ？
ﾋ彙窶堋ｵ窶佛?ﾅｽﾃｨﾂ：ﾂ？ﾂ？ﾂ 窶敖｢ﾂ？
Compared with:
ﾅｽﾂｩ窶｢ﾂｪﾂ：ﾂ催ｰ窶愿ｺﾂ、窶堋ｽ窶堋ｱﾂ湘??堋ｫ窶ｰﾂｮ窶堋ｳ窶堙ｱ窶堙??ｰﾃｯ窶堙≫?堋ｽﾂ人ﾂ．ﾂ．ﾂ．
ﾋ彙窶堋ｵ窶佛?ﾅｽﾃｨﾂ：窶堋､窶堙ｱﾂ。
ﾅｽﾂｩ窶｢ﾂｪﾂ：窶督ｼ窶楼ﾂ、窶ｰﾂｽ窶堋ｾ窶堙≫?堋ｯﾂ？ﾆ地ﾆ歎ﾂ、ﾆ地ﾆ歎ﾆ停?榿筑ﾂ？
ﾋ彙窶堋ｵ窶佛?ﾅｽﾃｨﾂ：窶堋?ﾂ、ﾆ地ﾆ歎ﾆ停?堡暖窶堋ｳ窶堙ｱ窶堙??堋ｵ窶堙･窶堋､ﾂ？
This was a very long post, but I figured you want too much information versus too little.
I'm quite serious about what I'm going to say: if you seriously follow this advice, you WILL become proficient in the particular dialect you are studying. Only pitfalls to watch out for are these:
1) Don't study all standard dialect (窶｢Wﾂ鞘ぎﾅ津ｪ) if you live in Kansai and want to speak natural ﾅ?ﾃ鳴青ｼ窶｢ﾃ (Kansai-ben, Kansai dialect). Same applies to other dialects.
2) Please don't speak like the NHK broadcaster! We'll all get a good laugh, but you won't, so be careful about studying too much of the NHK news (though it is useful for important political and social topics and vocabulary).
3) Don't spend too long on the same material. It may be easy to continue to watch that same episode of Bistro Smap, because you know it so well now, but there's only so far you can advance using the same stuff over and over.
4) Definitely supplement this study with some old-fashioned book learning. Don't just read novels and such, but also get a good grammar book and read it and study it, and practice the sentences in it out loud until it feels natural (no on-the-fly translation in your head, cause it won't cut it in the real world). For example, repeat this sentence without thinking of English until it just seems to "have" a meaning in your head:
窶堋?窶堙娯?彡ﾅｽﾃ俄?堙個人窶堋ｪﾂ、窶ｰpﾅ津ｪ窶堙ｰ窶｢ﾂｪ窶堋ｩ窶堙ｩ窶堙ｭ窶堋ｯ窶堋ｪ窶堙遺?堋｢ﾂ。
Then, start substituting different words in for 窶ｰpﾅ津ｪ. You can start with simpler things like changing to a similar noun (ﾆ檀ﾆ辰ﾆ団ﾅ津ｪ), and then get a little more advanced with 窶ｰﾂｻﾅ?w. Then, start replacing the whole phrase 窶ｰpﾅ津ｪ窶堙ｰ窶｢ﾂｪ窶堋ｩ窶堙ｩ with something else, like ﾆ樽ﾆ耽ﾂー窶堙ｰ窶册窶堋ｭ. Then, as much as you feel at least 95% confident of the language, start changing the structure a little more. Best method is to follow closely with the sample sentences in the grammar book, and then start searching for the phrase in Google or on ﾆ但ﾆ停?ｹﾆ誰's search engine. Always listen carefully and particularly stop at points in your audio practice where they use your newly learned grammar.
5) Systematically work through a vocabulary book, such as the ﾅ?ﾂｮ窶牢ﾆ筑ﾆ湛ﾆ耽ﾂー窶愿ｺ窶怒ﾅ津ｪ窶拿窶氾最ｽﾅｽﾅ陳ｱﾂ ﾅ津ｪﾅ澱 series. Fortunately, 1 and 2 are combined into a single book, so you can get a lot of awesome vocabulary from it. It's separated by type of word (noun, verb, adjective, adverb), so vary it up a bit. What I do is study one chapter for two weeks and do the practice exercises, then I change the type of word and study another chapter for two weeks. Recommend the same series for the grammar book.
6) Be on the lookout for two things especially: pitfalls that learners of your native language frequently fall into, and "avoided words." What I mean by the former is this: what words or grammar constructions are frequently used incorrectly by speakers of your native language? Also, what phrases or words are overused by speakers of your native language? Many English speakers far too frequently say ﾂ「ﾂ行窶堙≫?堙??堋｢窶堙懌?堋ｷﾂ」 to mean "I'm going/coming." They may also say ﾂ「窶藩??堙??堋｢窶堙懌?堋ｷﾂ」. What they don't realize is that these are states of what happened after the movement occurred, not mid-movement or ongoing movement. Additionally, many Americans rely too much on English word order style for their sentences, preferring to say A over B:
A: ﾅｽ窶樞?堙固ｽOﾂ人窶堙娯?認窶傳窶堙?窶藩??堙懌?堋ｵ窶堋ｽﾂ。
B: 窶認窶傳窶堙?ﾅｽOﾂ人窶藩??堙懌?堋ｵ窶堋ｽﾂ。
A: ﾂ十ﾂ人窶堙娯?慊ｯ窶板ｻ窶堋ｪﾂ食ﾅｽ窶凪?堙ｰ窶堋ｵ窶堙懌?堋ｵ窶堋ｽﾂ。
B:窶慊ｯ窶板ｻ窶堋ｪﾂ十ﾂ人ﾂ食ﾅｽ窶凪?堙ｰ窶堋ｵ窶堙懌?堋ｵ窶堋ｽﾂ。
As for "avoided words," these are things we prefer not to say because they aren't so sensible to us in our native language, or because we can't wrap our minds around them easily. They include things like the 窶ｹC idiomatic expressions: 窶ｹC窶堙娯?堋ｹ窶堋｢ﾂ、窶ｹC窶堙娯?愿?、窶ｹC窶堋ｪ窶伉≫?堋｢. They also include phrases like the use of 窶佚･窶｢ﾃ for good things (窶敕楪鞘?披?堙坂?佚･窶｢ﾃ渉青ｨ窶氾坂?ｰﾃ?, since we often learn 窶佚･窶｢ﾃ in a purely negative sense. Find the phrases that you hear and see a lot that you realize you (and your international friends) are not using, and focus on them for a while; learn to use natural phrases even if they don't make much sense to you as they are.
I hope this helps!
