Back in the day I had my fair share of hook ups / fwb relationships.

Most of my fwb started as random hook ups. We met, hooked up, both enjoyed the sex and thought each other were cool enough to hang out other wise. We usually hung out in group settings and didn't really spend time together 1 on 1 aside from sex. I wouldn't say they went 100% smoothly but were generally pretty successful and usually just fizzled out or ended because the situation was no longer convenient (went to college out of town, got back with gf, that kind of thing)

There was one case where the friendship came before sex but it ended badly and I wouldn't recommend it. Unknown to me he had romantic feelings and drunkenly made a move one night.. I took it as drunken fun. We continued on for a while but the whole time he was hoping it would turn into more. Not pretty. We still have mutual friends and years later things are a still little weird.

When I was consistently hooking up with a fwb I didn't actively have sex with anyone else but would still flirt and make new friends. But if we hadn't seen each other for awhile or things were winding down / not going well I did what I wanted.

But definitely talk about it with them. A fwb relationship can go south really quickly if you don't know where each other stand. If you really are swooning over someone, even though it's tempting don't have casual sex with them. Keep it light and have fun!