One thing that sets Japanese culture apart from many others is the usage of set phrases. Well, it's not like we don't have set phrases in English, but you probably don't notice them because there seem to be so many ways to say the same thing in English: see ya, goodbye, ciao (okay not English, but meh), catch ya later, bye bye. You get the drift.

There is a lot of room for flare and variation in the huge range of English set phrases. Japanese set phrases on the other hand generally don't have variation to this degree. In a certain situation, the only thing to say is what you say. More or less. I'm covering my bases here, trying not to overgeneralize, but at this moment in time I feel that this is correct. Anyway, let's go through a couple of set phrases, in no partiuclar order, except the order that they popped into my head:

• 初めましてhajimemashite - When you meet someone for the first time, you say this, followed by your name, company, nationality, favourite Spice Girl, whatever. It often gets translated to the English how do you do, but come on, who actually says that?
• お早うございます ohayou gozaimasu - Basically this one means good morning. The word for early comes up there, with an inflection that isn't really used too often anymore. You use this in the morning, after you see someone for the first time that day. Each consecutive time, you just do a little bow, or head nod called an 会釈 eshaku. Another time to use this phrase, regardless of the time of day, is when you start work. You greet the other staff with this saying (make sure to greet everyone too). In a non-formal situation, it can be shortened to お早う ohayou, or even to おす osu among friends.
• こんにちは konnichiwa - Similarly, this word means good afternoon, as a daytime greeting. Literally means 'today.' Usually written in hiragana. May be seen as こん kon on some internet chat sites.
• こんばんは konbanwa - An evening greeting; good evening.
• お休みなさい oyasumi nasai - Means something along the lines of have a good sleep. Say it when you say goodnight and part with someone. Can be shortened to お休み oyasumi among friends.
• ありがとうございます arigatou gozaimasu - Thank you. Can be shortened to ありがとう arigatou among friends, or lengthened to どうもありがとうございます doumo arigatou gozaimasu in a formal situation. A funny way to say it, あざあす azaasu is used very casually, usually to the coach of a sports team. Strange, I know.
• すみません sumimasen - This word is very useful. Bascially, whenever you've done something wrong, this word will be there to wipe it all away. Bascially sorry, but can extend to the meaning of thank you also, for example when recieving something. Sometimes takes the form すみませんでした sumimasen deshita in the past tense. It can also mean excuse me, when trying to get someone's attention. It is polite, but trusst me, it's damn annoying being called over by sumimasen every 10 seconds.
• 失礼します shitsurei shimasu - Quite literally I'm being rude. Used when you are imposing on someone, so can also mean excuse me, for example when you need someone to move out of your way. It gives the listener less chance to refuse than sumimasen On a side note, if you fart, you can say 失礼しました shitsurei shimashita.
• お邪魔します ojama shimasu - Literally means I'm intruding. You use it when you enter a room, or even someone's car.
• ごめんなさい gomen nasai - Sorry. A little more personal than sumimasen. Usually used between friends in the form of ごめん gomen.
• ごめんくださいgomen kudasai - You use this when you enter someone's house and are trying to find out where everyone is. Bascially used in place of may I come in?, or is anyone home?.
• お疲れ様です otsukaresama desu - Comes from the words meaning tired and person (sorta). The meaning is tough, I guess something like you must be tired. You say it to your workmates when you finish work.
• ご苦労様 gokurou sama - similar to the above, except on people of higher-status can say it to lower-status people. Imagine a boss saying good work.
• お先に失礼します osaki ni shitsureishimasu - Used after you finish work before other people. Like I'm rudely finishing before you.
• 申し訳ない moushi wake nai - When you've done something (or going to do something) so terrible that sumimasen just won't suffice, you can bust out this trump card. Literally means there's no excuse.
• いらっしゃいませ irasshaimase - You'll hear this one when you go into a shop, literally it means come in, but I guess welcome more aptly sums it up.
• 毎度ありがとう maidou arigatou - You may hear this when you leave a shop. It carries the meaning of please come again, and also thank you. Yamapi shortened this to 毎度あり maido ari in the drama Kurosagi.
• 頂きます itadakimasu - Before you eat a meal, put your hands together in a quick praying motion and say this. The literal meaning is to recieve, as in recieving food.
• ご馳走様でした gochisou sama deshita - The counterpart to the above. Said after a meal, and translates well to it was a feast
• 遅くなってすみません osoku natte sumimasen - While not exactly a set phrase, it is a useful one! It means sorry I'm late!
• お待たせしました omatase shimashita - You'll hear this in a restaurant. While it does mean I've made you wait, they will probably say it no matter how speedy their service is.
• 畏まりました - kashikomarimashita - Also in the restaurant or service industry, meaning certainly.
• どうぞよろしく douzo yoroshiku - This one is lame when translated to English. It comes out as a nice to meet you, but really that's not super correct. You say this after you meet someone for the first time, after your introduction. It carries a meaning also of look after me, or something similar. Tough one. Can be lengthened to どうぞよろしくお願いします douzo yoroshiku onegaishimasu for that extra bit of formality.
• よろしく yoroshiku - This can be used to mean something like I'll leave it up to you when telling someone to do something. Like above, you can add お願いします onegaishimasu to pump up the politeness. It may also convey the kind of meaning of let's work well together. Tricky.
• 只今 tadaima - This is a shortening of the phrase 只今帰りました tadaima kaerimashita which literally means I got back just now. You say it after you get back home after going out, funnily enough.
• お帰り okaeri - What you say to a person who says the above, meaning welcome back. Gets shortened to オカ oka on some internet chat rooms.
• お世話になりました osewa ni narimashita - You say this when you leave someone (for a longtime, or forever) who has taken care of you. It can be interpreted as you've really taken care of me.
• 迷惑をかけてすみません meiwaku wo kakete sumimasen - Borrowing from our sumimasen from above, this adds meiwaku, meaning trouble, and the result is I'm sorry for causing you trouble
• 行ってきます itte kimasu - You say this before you leave somewhere that you plan to come back to. In that sense it means I'm leaving now (but coming back).
• 行ってらっしゃい itte rasshai - The response to the above. Directly translated it's a polite way of saying go and come back. Interpret that how you will.
• つまらない物ですが tsumaranai mono desu ga - We westerners tend to make our gifts to others seem like they were more expensive or great than they are, but Japan is the opposite. When you give a gift in Japan, you say this, it's nothing interesting, but... Even if you think it's the greatest thing in the universe!

Any I should add? Comment please.