Greetings and Such

Here are how to say some greatings in Japanese:

おはよう	Good Morning
こんにちは	Good Afternoon
さようなら	Good Bye
おやすみ(なさい)	Good Night
ありがとう	Thank you
すみません	Excuse me / I'm Sorry
いいえ	No / Not at all
いってきます	I will go and come back
いってらしゃい	Please go and come back
ただいま	I'm home
おかえり	Welcome Home
いただきます	Thank's for the meal
ごちそうさま	Thank's for the meal
はじめまして	How do you do?
よろしく　おねがいします	Nice to meet you

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You can add ～ございます to the end of some words to make them more polite. The words in this list that this work with are:
おはよう ==> おはようございます
ありがとう ==> ありがとうございます

The parenthesis in some words are used to show that the word can be said either way, one of which just being shortened.
おやすみ(なさい) ==> おやすみ or おやすみなさい
おかえり(なさい) ==> おかえり or おかえりなさい
ごちそうさま(でした) ==> ごちそうさま or ごちそうさまでした

いただきます and ごちそうさま(でした) mean the same thing, but いただきます is used before a meal and  ごちそうさま(でした) is used after.

いってきます and いってらしゃい are used when someone is leaving their house.

はい and ええ both are for yes, but ええ is more casual than はい. When using short form, you will find that うん is more casual than ええ, so I normally use just はい and うん. はい can also used to respond to what someone says, such as a teacher calling your name, and in cases when someone knocks on a door; the person inside would often call はい to respond to the knock before they make it to the door.