I want my Japanese writing to sound normal. Not like it was written by a foreigner.
Suggestions?
Wanting to sound "normal" is a tough task. When people say that it's "okashii", normally you used the wrong words or you used stiff and/or old fashioned words/phrases. There are basically 2 ways to sound more "natural" and "normal", the quick way and the slow way.
Quick way: Learn short common expressions as-is. e.g. Try memorizing "ringo ga tabetai na" instead of "ringo wo tabetai" (although both are correct but the latter is used more often in writing).
Learn COMMON conjunctions (e.g. to itte) and collocation (e.g. yori ni yotte)
Try breaking down sentences into smaller fragments. Try to avoid long relative clauses. Making a ultra long sentence won't necessarily be a way of demonstrating your masterful Japanese proficiency. More often than not it would just confuse the listener.
Mimic how natives speak, and note the word order of their sentences. e.g. casually, people usually say "abunai janai? kore.." instead of "watashi wa kore wa abunai to omoimasu".
Understand the culture in greater depths. e.g. direct vs. indirect passive voice, or when to use which specific reading (like momiji vs kouyou or furusato vs kokyou)
Slow way: Learn commonly known idioms. e.g. neko wo kaburu, hone wo oru etc.
Learn compound verbs. Last time I asked there are at least 1000 words that you should know.
Learn onomatopoeia. It's hard and not particularly effective to use flashcards for this, unless you have also written down sample sentences on them. The problem with learning this is that many giongo and gitaigo can only be used in specific situations. giongo and gitaigo would make your speech more lively, but won't necessarily make it more "natural" though.
Learn phrases/words (through tv etc) that you otherwise wouldn't be able to learn if you live in a foreign country, but nevertheless can be important. e.g. "ホッチキスでとめる" (to staple something) "水を流す"(to flush the toilet) "ボタンを留める" (to fasten your buttons)
Read more.
The best way though, is to find the books and resources that will give you info on these finer details. Many language books nowaday are rehashes of one another. Many books go into how wa is different from ga, or give very long explanations on how to differentiate tara, ba, to, nara etc. Yet, so few books actually provide tips on how to fine tune your Japanese. Common phrases like " ためになる" "気持ち短めに" "電話に出る" "買って出る" " 会社のつけにする" are normally not found in your standard text, and can only be found in less mainstream teach-yourself books, so you will have to dig deep in order to find these treasures.
Good luck!