Once you build up the courage for oral, here are a few tips:
1. Don't deep-throat. Don't even try. Why gag for no reason? Men get stimulation from envelopment and your mouth on the head of their penis. Use your hands to encompass the rest of his shaft and focus your sucking power on the head!
2. Use LOTS of spit. Oral is not a clean pretty act; it's rather messy and slimy.
3. Pay attention to HIM. Try all sorts of things; suck harder, use more spit, flick your tongue, switch to hands. A newbie at oral who actually pays attention to the guy will actually give a better blow job than a girl who thinks she knows what she's doing and ignores the man's responses!
4. Swallow. Just a personal thing; obviously if it's just disgusting tasting then spit. However, I've swallowed every single time I've ever given oral, even the first time.
5. Punch him in his privates if he dares to try and force your head down or tries to force you to deep throat!

[edit] Or better yet, BITE him!
6. On the subject of biting, some guys do actually like a bit of teeth. Ask, or hopefully, he'll tell you.