For anyone that wants to seriously learn Japanese you should first memorize this. The hiragana alphabet. Once you have this down you can read children's books! Exciting, yes? xD

Also here are some common phrases and the romaji to go with them. You have undoubtedly heard them in anime before. XD
こんにちは. [konnichiwa.] Good afternoon
おはよう。 [ohayoo.] Good morning
おはようございます。 [ohayoo gozaimasu] Good morning (polite)
こんばんは。 [konbanwa.] Good evening.
さようなら。 [sayoonara. ] Goodbye.
おやすみなさい。 [oyasuminasai.] Goodnight.
ありがとう。 [arigatoo ] Thank you.
すみません。 [sumimasen.] Excuse me/I'm sorry
いいえ。 [iie] No; not at all
はじめまして。 [hajimemashite] How do you do?*
どうぞろりしく。 [doozororishiku.] Nice to meet you.
* for hajimemashite, this is only used for first introductions. You do not use it for people you have met before/know well.