How to prep for taking it

Hi- this is my first post here, so I hope I’m doing everything right. I’ve got a question that I hope someone can help me with.

I want to try bottoming for someone I know, but I don’t know how to prepare correctly. We’ve hooked up before, which is why I feel more comfortable trying it. This would be my first time taking a cock in my ass, so I’m a little nervous both in terms of size and being cleaned out properly before. I know we cab go slow and careful for the fitting it in, but I’m mainly just unsure how to get myself ready in advance.

Any advice at all is appreciated. Thank you!