While alot of women don't mind giving oral, some fade out on doing it for many reasons. For one, be vocal and moan about how much you like it. Keep in mind that if you are great at pleasing her, she might just reciprocate by giving you more oral.
Here is some tips that many women already know, but which might be able to help.
First off, "Men, relax and just stay still!" Especially if your woman is not used to giving much oral. Let her learn not to gag. At least not yet!
Ok, ladies, pretend your mouth is hungry and ready to ravage his world.
Alittle drool as you suck is always nice, as most men like it a bit nasty. "Always a lady outside of the house and a whore in bed". At this you will have ruined him for anyone else.
Experiment with hand around, then have your head up and down in like a circular or nodding-like movement. Do it wild and look up at him, they love this! Ofcourse, no teeth, unless you're mad at him......he-he, just kidding!
You can also numb your throat with a throat-numbing lozenger or products made just for this. These products might in turn delay his climax, which would be your goal if you really want more sex afterwards. This lozenger can help you with relaxing your throat and controlling your gag reflex. Going down further is not something I can tell you how to do as it is NOT for everyone. But, in time, you can learn to deep-throat, if you wish. Really, the most sensitivity is closer to the tip to 1/2 of their shaft, so not a big deal. You can put a strong vibrator under your bottom lip to make vibration as you suck as well as moaning to vibrate your mouth.
Alot of men have this thing about you swallowing his cum. If, for some reason, his cum is really bitter, like an aspirin, just swallow a little bit and drool some of the rest. Hopefully for you, he will be salty or sweet, not bitter. And you can smear it on your face. He might like this but you might say ewww!! Supposedly alot of people say semen is good for preventing wrinkles and acne. The good news is that it is LOVE JUICE!!!!! A product of LIFE........... so enjoy it. If you do not enjoy oral, you can just pretend. Our secret, because so many women have done this for years.....lol...............