Start by lowering yourself to your knees and crossing your arms on the ground in front of you, using a pillow to cushion your elbows. Stick your butt in the air and rest your head on your arms, bracing it on the floor if you need to. Tell your partner to stand behind you and lift your legs up by your ankles until your body is almost perpendicular to the floor. Keep your knees bent and have him enter you from behind.
This is almost as tough as it gets because of the yoga-factor, but if you can nail it in you're in for a world of fun.
You'll love it because
Two words: deep impact. This position has all the benefits of any rear-entry move, with the bonus of gravity on your side. Plus, your practically upside-down body position will give the whole new perspective on your sex life.
Have him swivel his hips while he's inside you. The combination of the new angle and the added movement will trigger some sensitive spots you never knew you had. His penis will be stimulated from every angle, too, ensuring a mind-blowing climax for the both of you, and maybe even at the same time.