
Biggest thing is communicate. It'll be a little awkward to ask during the act, but she will be able to tell you what feels good and what doesn't. Next biggest thing is listening to what she tells you. Best tip? Ask her to be vocal during the act. Tell her she controls your speed/ pressure during the act. If you she does that, and you listen, you can ensure she gets what she needs out of it.
Communication is key. If it's her first time, start off slow. Actually, start slowly even if it is her subsequent time. Go in with your palm facing up towards you and curl your fingers up. You could keep your fingers straight but curling them up and doing the come here motion is something they really tend to like because the G spot is in that general location. Don't be afraid to ask if she likes it or not. It's not fun if you're both not enjoying it.