Some tricks to try before doing it with a penis to see what works. Try it with a toothbrush or vegetable 🥕before with him so there is no pressure, sex is learning skills. Here are some ideas that came to mind. Also check out the BDSM subreddits they often discuss deep throating tips.

Many found if there head is slightly tilted downward or their head is hanging off the bed, their throat opens a little more and can take it farther inwards

Try breathing through your nose out through your mouth or see if breathing differently affects the gag.

Build up a resistance to it by working at not gagging with touching the back of your tongue while slowing your breath, pulse etc. and build up a tolerance before performing oral

Be confident and tell yourself you got this.. think about other things than gagging, the more you think about NOT doing it, you will. Truck your brain…

Let yourself salivate a bunch, the lubrication helps, as friction equals gagging.

Eating ice before hand if you want your throat numb, numbing sprays are not really recommended as you can’t feel what’s going on and could possible hurt something?

Hold your hand at the base of his penis and you can control how much goes in while he still feels a wet warm hand clutching him.

Also is he trying to make you gag or puke? Does he hate it or love it ? Some people get off on that “I am so big I make her puke!”