Say what you'd like to try
Talking about what you like and dislike has several benefits. Not only can simply talking about sex add to your excitmement, but the more you talk, the more relaxed and confident you'll be with your partner.

Be honest, positive and demonstrative
If you're going to say what you'd like and ask what your partner wants, there are three important points to keep in mind.
Be positive. Don't tell your partner they're terrible in bed. Remember something they did that you really liked and say, "When you did that, I really..." They'll get the message.
Be honest. There's no point in faking it or saying you like something you don't, because that gives your partner no incentive and no guidance to do better.
Be demonstrative.