I would suggest playing with your own bum first, and getting comfortable with it. then you'll know what to expect. Just stick your finger in a little in the shower and work your way up from there. then when you have anal sex you'll know how to relax your muscles and won't be as nervous. I think in general self discovery=better sex in the long run. and don't be afraid to put on the breaks if things are going too fast or you need some time to get used to a sensation. you can always start up again later. good luck and have fun!
