Answer:
The one best thing to do is signal your partner when things are feeling good. "Oh yeah, that feels great!" "Do that some more." or just a happy moan. Encourage them to do the same.
The next best thing is to talk about what works. We're all taught not to talk about sex, but that rule DOES NOT apply to lovers. You are free to talk as much as you like about what turns you on. It's important for the two of you to believe that sex is supposed to be fun for both of you!