"I'll tell you what I want, what I really really want,
So tell me what you want, what you really really want."
Spice Girls lyrics may not have always made the most sense (what is zigazig ah?), but they got a few things right. The lyrics above from "Wannabe" serve as a reminder to communicate before and during sexual activities. (It may not have been the intention, but that's how we see it, at least). Tell your partner what you want and ask your partner what they want, as well. So how does that happen?
Keep lines of communication open.
Avoid judging your partner for what they are interested in.
Be clear about your own boundaries.
Respect your partner's boundaries (and your own).
Do what you can both agree on and consent to doing together.
Talk it out.
If something uncomfortable starts happening, address it rather than letting it sit and stir below the surface.
Tell your partner what's happening and listen to your partner in return.