One thing I will tell you is this, I don't know if there is any one way to learn Japanese "quickly". I'll give you a bit of advice that probably would have saved me a lot of time if I'd been told. A lot of books, for example, one like "Japanese Step by Step" (which you should avoid) for example, will try to map each Japanese language convention to its English counterpart. While this works for some things, it's misleading or confusing for others.
For example, the way we think of nouns is as a sort of person, place or thing, an example (from wiki), "
Apple is both a
computer company & a
fruit".
Now look at this sentence in Japanese:
あなたは英語を勉強していますか。 (Are you studying English?)
anata wa eigo o benkyou-shite imasu ka?
eigo (English) is a noun, but so is benkyou (to study, diligence), with the addition of the verb
suru (to do) you have a verb form that means 'to study'.
Adjectives work in a similar way. Basically what I am saying is that it's important to learn
Japanese, while avoiding using English as a proxy to communication as much as possible. When learning how to speak Japanese, avoid composing an English sentence that you wish to convey in Japanese--- simply learn the myriad ways that you can communicate with coloquial Japanese.
That said--- get a good book w/ a workbook & audio. People say nice things about
Genki.
Learn the basic
writing systems, hiragana & katakana, a set of characters (rather a Syllabary) each of which represents a sound in the Japanese language. You'll want to rely on this first and foremost, instead of roumaji (romanized japanese such as
nani o shite imasu ka?, and the example above).
From there you'll learn the Kanji, grammar, how to construct sentences, particles, and find that you never ever really
stop learning the language...
See if you can find a language
meetup near you, it's incredibly helpful to have a native speaker whom you can ask questions.
By all means, make learning the language FUN... Incorporate it into things you do, like learning songs you listen to, or movies you watch. The best way to learn Japanese is to have a good time learning it--- to make it fun for you--- I think this is the best motivation of all, to really want to learn the language each day.
Good luck.
