Before discussing particular particles (pardon the pun) we should first consider the topic of word order. Japanese word order is fairly free, but there are some restrictions. The language uses SOV word order, i.e. Subject first, Object second, and Verb at the end. This contrasts with English's SVO word order.
おとこ は いぬ を かじる
"Man bites dog"
In the above example the subject is "man" in English, "男" in Japanese. The object is "dog" in English, "犬" in Japanese. The verb is "bite", "かじる".
Japanese sentences can be roughly divided into three major categories, 'action', 'existence', and 'motion', based on the meanings of their component verbs. In general, word order in Japanese sentences using an action verb is:
あした、がっこう で せんせい に プレゼント を あげます
"[I'm] going to give a present to [my] teacher at school tomorrow."
For an existence verb it is:
たかはしは、いま ほんしゃ に いる
"Takahashi is in the main office right now."
And for a motion verb it is:
あした、パーティ に いく
"I'm going to a party tomorrow."
SUBJECTs are put in brackets to stress that they are very often deleted. In general, if a new subject is introduced where another had been previously understood, signal the change by placing は after the subject. If a subject is understood but for some reason not deleted (which is rare) use が or nothing.
Often you can move the subject to the end of the sentence, following the verb, when other parts seem to be piling up excessively. So:
あした ぼく が こうえん で うたう
"I'm singing at the park tomorrow."
あした こうえん で うたう、ぼく
"At the park tomorrow I'm singing."
For more on SUBJECTs, see the longer description in the next section, Subjects and Deletions. Knowing how and when to delete subjects is a key to speaking naturally.
TIME is usually followed by に. In general, use に for specific points in time or specific spans of time. So "十月に" (じゅうがつ, "October") and "三月三ヵ日に" (さんがつみっか, "March 3rd") both take に. A word like 明日 (あした, "tomorrow") that can only be understood by context (because it changes depending on when you say it) is called 'deictic'. Deictic time words don't take に. Thus "明日行く" (あしたいく, "I'm going tomorrow."), but "三時に行く" (さんじにいく, "I'm going at 3.") Even if you have trouble making the distinction between these two types of time words, don't worry: Japanese people can understand what you mean even if you get it backwards.
PLACE/IMPLEMENT is followed by で. A PLACE is the location that a volitional action occurred. If you're eating at home, that's "お家で食事する" (おうち で しょくじ する). If you're eating with chopsticks, that's "お箸で食べる" (おはし で たべる). The place you do something or the thing you use to do something takes で. If you're going somewhere by car, you say "車で行く" (くるま で いく). It's not that hard to understand really. (See INDIRECT OBJECT for why DESTINATIONs are different.) Verbs of motion that tell DESTINATION, or ones of existence that tell the LOCATION of something take に. DESTINATIONs can also take へ. Try to distinguish PLACE from LOCATION by thinking of it this way: PLACE is where something is done, LOCATION is where something or someone is. Use から ("from") after an ORIGIN and を after a ROUTE.
がっこう から、こうえん を とって、おうち に かえる
"I'm going home from school through the park."
The particle まで can also be used with DESTINATION, particularly when comparing or contrasting it to ORIGIN. Both から and まで together form a pair much like "from/to" in English.
OBJECT is followed by を or nothing. "本を読んでいる" (ほん を よんで いる, "I'm reading a book.") This is a really simple one in most cases. Few Japanese learners seem to have a problem understanding this. The only difficulty you might encounter is differentiating between this OBJECT and the INDIRECT OBJECT.
INDIRECT OBJECT is followed by に. An INDIRECT OBJECT is a sort of secondary object that some verbs take. "この本をあなたに上げる" (このほんをあなたにあげる, "I'm going to give this book to you"). You have "this book" and you have "to you". The phrase "this book" is the OBJECT. The phrase "to you" is the INDIRECT OBJECT. Particles を and に are used to distinguish the two.
VERB doesn't take any particles but it does need to be conjugated. There's a separate section on verb conjugations below, which see.
|SUBJECT + は/が/nothing||delete subject if possible, show changes with は|
|TIME + に/nothing||use nothing if it's a deictic time word|
|PLACE/IMPLEMENT + で||is the place where you do or where you are?|
|LOCATION + に||is the place where you are or where you do?|
|ORIGIN + から|
|ROUTE + を||is this a place on the way to where you're going?|
|DESTINATION + に/へ||use に over へ but be aware that both are okay|
|INDIRECT OBJECT + に||use this if you're out of choices :-)|
After understanding the descriptions given earlier, these nine lines are the key to knowing what particle to use 90% of the time. Even if these rules cause you to make a mistake you'll still be understood.