How can I tell him how I like it?

I'm having terrible time telling my boyfriend how I like it. I'm nervous of how he is going to react to me doing these or bring up the some ideas.

I don't have a whole lot of confidence relate to the fact that he is training to be a body builder and I am athletic and go to the gym regularly, but still not considered swole yet.

How can I possibly tell him what I like easily?