I have trouble with this too (my partner just isn't very vocal, and I'm a bit shy at times). And I agree with kadelette's idea- to ask questions that will lead to the answers you want.
A good thing to keep in mind with anything you want in the bedroom is to talk about it during a time not related to sex. This gives your partner the freedom to discuss any doubts, and not feel obligated or uncomfortable.
Also, just try to relax and take a deep breath before you talk to him. I'm sure he will appreciate your honesty about it (particularly if he knows you are shy and that it is hard for you to talk about) and want to try new things with you to make you happy.