First time for anal. Tips?

So, my SO and I are thinking of trying anal for the first time. He has done it before with other partners (him to them) but I have never done it before.

I’m worried about being “clean” I guess? Since I’ve never really known anyone whose done anal and I’m not a huge porn watcher, I don’t know what to expect.

I did have an incident where another ex boyfriend accidentally entered there, and it was so painful I screamed (not in a good way lmao).