Anal sex beginner

So I've never had anal with my bf but we were talking about fantasies and I asked him if he'd want to try it.. he said yes.. but I'm not sure if I want to, but not because of the actual activity more because I'm worried about the messiness of it, what it's supposed to be like.. like what do I expect during it and how can I prevent it from being just gross.. like I feel like shit gets everywhere which sounds silly but Im curious if anyone can give me advice on what to do or expect before or during anal sex?