But let's cover some anal play basics:
1. You don't need to have an enema first, but sometimes it helps people feel more relaxed. You can buy a Fleet enema for 99¢ at the drugstore, and put in plain water for an anal douche. Do this at least an hour or two before you start fucking.
2. Use plenty of lube. Spit is not enough!
3. Fingers, tongues, cocks, and sex toys with flared bases go up people's asses. Don't put other stuff up there.
4. Wearing a latex glove can make everything slide better if you want to fingerfuck your lover, and cleanup is easier too. (Ditto condoms on sex toys.) If you have long fingernails, put a cotton ball in the fingertip of each glove.
5. Start small and work up. Nobody takes a big ol' silicone cock up their ass the first time out. Get a slender dildo, or use your finger(s). I recommend doing several different sessions of butt play, starting with finger penetration the first time, and on the next occasion trying a small dildo and getting comfortable with that, even over several sessions, before progressing to larger toys. Go slowly with the movements, too--save the fast and furious fucking till you're both more experienced.
6. A suggestion: Butt toys that vibrate feel good, and help relax the muscles.
7. Educate yourself about STDs, and take whatever precautions are appropriate with your partner.