How to play with his ass...

So my husband just told me he wouldn't mind me trying to play with his ass. He has friends who told him it feels amazing so i'm pretty sure that's why he wants to try it. I NEED TIPS. I have NO idea what i'm doing. I assume I'll probably start out maybe fingering his ass while i'm giving him head but he's always laying down on his back when I do that so how would I get to his anal area? I need ideas ladies tell me what you do with your mans ass that he absolutely loves!