Giving or receiving? If giving, just pretend you're sucking raw oysters. Alternate sucking, licking, and blowing air onto the hole. If you really want to get into it, ask the recipient to push out a little and suck the hole. If you're feeling more creative, write the alphabet using your tongue. Some guys like their hole slapped a little, and you can do this using 1-3 middle fingers. If you're in a monogamous relationship and you and your partner don't fuck around and are both HIV neg, slight biting is OK, but exercise prudence so that the anus doesn't bleed. I could write an essay on this, but you'd have to pay me for it.