Don’t scrimp on the foreplay. Foreplay will never go on too long for her. I don’t mean that no amount of time is too long, I mean that when she’s done with foreplay, she’ll be desperately pulling you on top of her and putting you inside, so don’t worry about doing too much of it. She’ll let you know.
Don’t put all your weight on her unless she says it’s okay. Most men weigh enough that pressing all of their weight on a woman will crush her ribs, or, if nothing else, make breathing difficult.
Don’t lean on her hair either with your hands or your head. Move her hair out of your way first.
When she’s doing something you don’t like, say something. But rather than say “no” or “stop,” which can be insulting, give her direction about what you do want. Directions during sex that are given in the affirmative (“I really like it when you xxx”) rather than the negative (“Doing xxx does nothing for me sexually”) are much more helpful (to both you and her), and won’t hurt her feelings because you’re not telling her she’s doing something “wrong.” No one likes to be wrong sexually.
Let her initiate going down on you. Do not pull or push her head down. Sometimes a woman doesn’t feel like doing it, and some women never want to do it. Never force or coerce her. This will set you apart from other men and show you as a better lover. Appalling that some men are so inconsiderate. But true.
Afterward, consider asking if you can get her anything.
Staying awake for snuggling afterward can be nice. If you are going to fall asleep (as many men do and most experienced women understand), say something so she doesn't feel ignored or used—like “You were so amazing, you've worn me out.”
Jumping up to take a shower or wash the smell of her off your mouth, hands, etc. will make her feel dirty, and like you really didn’t want to be going down on her/touching her. But don’t be insulted if she jumps up and runs to the bathroom right after. Some women get urinary tract infections quite easily and peeing after sex helps avoid UTIs.
Ask her what you could do more of next time and tell her what you liked in the afterglow of sex--not like two minutes after you’ve orgasmed but five or ten minutes. Don’t be afraid to ask more than once. Just not every time. Every time makes you seem insecure… You could say something like “You seemed to like [this particular activity], did you?” or “Is there anything I could have done more of?”