I'd have to agree with the other ladies that overcoming the gag reflex is mainly practice with a little mind-over-matter thrown in. And talking to your man might not hurt either. I was dating a guy that was huge and no matter what I did I could NOT deep throat him. I finally brought it up to him and told him that I had no problem performing fellatio and that I actualy enjoyed it but that if he tried to deep-throat me again then he was going to have regurgitated Taco Bell in his lap.
Anyhoo, he understood and still enjoyed my blowjobs. At least he said he did.
And my hubby enjoys my blowjobs (as I found out by accident - don't ask). Okay enough patting myself on the back. The point here is practice and don't be afraid to talk to your lover about it. Oh, and don't let him come in your mouth. If you are already having a gagging problem, that'll will probably push you over the edge. (actually, you probably already knew that or have already experienced it, so I'll shut up now
)
Good luck, btw.