There are lots of great resources in the sidebar/FAQ, which I highly recommend!

Also, I'd recommend telling him up front: "Hey, I'm excited about blowing you and learning some new skills—but I have no clue what I'm doing and would love tons of feedback and suggestions of things to try!" Personally, one of my greatest fears is giving my partner a mediocre sexual experience, but him being too polite to correct me, so that I think I'm much better than I am and never improve. I'm always asking for feedback, and paying close attention to his nonverbal signals.

And truly, the value of enthusiasm cannot be overstated. Even if you feel totally uncertain, look like you're excited to be down there and the charm will honestly win out over the dorkiness.