Masturbate and masturbate often. Alone AND WITH YOUR PARTNER (this is key as people react differently to different stimuli, and you will be stimulated in a quite different way with a partner than you will be alone.). Also, as Mr. Savage loves to point out--vary your techniques. Try to get used to a number of different sensations. There are products on the market now that attempt to mimic the feel of vagina, anuses, and even mouths. The closer you can get to the actual feeling of various types of sex, the more you'll get used to it. Good luck, and remember to talk your partners about this issue, and not to get embarrassed. Communication is key!