All I can tell you, is the first few times I did it, I thought I was going to throw up. Eating cum (especially out of a wet pussy) is not the tastiest or nicely textured thing to eat. Like escargot, though, it becomes an acquired taste. The more you eat it, the more you won't gag. lol.
Just jump in and do it the first time (and you'll get rid of those inhibitions). After that, it becomes easier and easier. Although, I must confess, I still don't really like the taste or texture of cum and really focus my mind on how humiliating it is to eat it while I'm doing it. You can also practice be swallowing some of your own.