A backhand is thrown by gripping the disc, top facing up, in the dominant hand (the one you feel most comfortable throwing with). In gym class, you may have been taught to place your index finger along the edge of the disc (other fingers curl up under the disc) and upon release, point to where you are throwing as a means of boosting accurately (as seen here).
This is acceptable, however if all fingers (except the thumb, which remains on top of the disc) are tucked under the disc, the power you possess and the distance you can throw will be increased dramatically. You will have better grip and can develop equal amounts of accuracy with practice.
Important things to remember when throwing a backhand: keep your release level. If the disc is level when it leaves your hand, it will fly level. If you are getting nasty hooks (disc flies sideways), time your release so that the disc is level when it leaves your hand. Another thing that will ensure beautiful backhands is knowing that it's all in the wrist. The more that disc spins, the more air it slices, and the father/straighter it will fly. So, upon your release, make sure that your wrist is doing its fair share.
The best way to consistently throw perfect backhands? Practice. Go throw with anyone you can find, and the more often you do it the better you will get. Also, using a quality disc can work to your advantage (see It's All in the Disc). But practice makes perfect, so be it with your team, your mom, or that guy that hangs around Burger King, get out and throw!
Bonus Material: Please try this at home!