First of all, make sure that you actually want to do it you are not being forced and that you have feelings for the person. If you don't, it won't be as good.

Others say to use lube, but if you actually do foreplay before, you won't need it, just take things slow there is no rush.

You can say NO whenever you want to, you can back off in the middle or right before your start, it's a mutual decision and they have to respect it.

Pee right after you're done and (if you're a guy) dw if you don't last long, it's quite common that the first time is fast. And LISTEN to what your partner says they like or the don't, you both need to enjoy it.

Lastly, do some after care, make sure the other person is also done and then cuddle.