I mostly learned these from watching anime, but was also taught in a japanese conversation class:
- Yatta (I did it!): Use when you accomplished something big, receive a great opportunity or feel victorious.
- Honto (Really?): Use it to confirm what you've just heard.
- A, so desu ka? (Oh, I see): Use it every time your conversational provides a new piece of information. Be sure to nod as you say this expression.
- Mochiron (Of course!): This is the favorite adverb of confident people. Use it when you are confident of your opinion.
- A, yokatta (Oh, good): Use it every time you feel like saying "What a relief."
- Zenzen (not at all): Suppose someone asks you, "Am I disturbing you?" when he's not bothering you at all. Say it and shake your head.
- Doshiyo (What shall I do?): Use it when you are in a panic and have no idea what to do.
- A, bikkurishita (What a surprise!): Use it when you are very suprised.
- Yappari (I knew it would happen): Sometimes you have a vague suspicion that something will happen, and then it actually happens.