The rest is just practice.....practice....practice...
IMHO, its ALL practice. Hueyracer's advice may be useful for initial training, but in the event of a for-real auto, you'll have to start with what you are given re speed, altitude, wind, etc and make adjustments to deal with the circumstances. One of my instructors is in the practice of covering the flight instruments during autos, and insists that the whole maneuver should be performed looking out the window and "listening" to what the rotor is doing. Too much practice using a "mechanical" technique may actually be counterproductive. Let me be quick to add that I am still learning how to hit the spot. Repetition seems to be the most useful approach.