Advice Column:
Play Controls tutorial:
Don't think there is only one "best" way to set up the controls and your hands. Here are a few techniques I've heard of in the past:
One handed, using 3 fingers on the arrow keys (Left, Up/Down, Right)
One handed, using 4 fingers on the arrow keys (one on each arrow)
One handed on the number pad.
Two-handed on the arrow keys. One index finger on each hand (representing the left and right legs)
Two-handed on the number pad. One index finger on each hand
Two handed on the arrow keys. Two fingers from each hand, one finger per arrow.
Two-handed on the number pad. Two fingers on each hand, one finger per arrow.
Two handed spread across the keyboard, assigning LEFT to A, DOWN to S, UP to K, and RIGHT to L. Left middle finger on A, Left index finger on S, right index finger on K, right middle finger on L.
One-handed in the middle of the keyboard (F,G,H,J).
Two-handed in the middle of the keyboard (F,G,H,J).
There are probably others which I haven't heard of but I have seen All of these techniques for playing Stepmania on keyboard. My personal preference is:
Two hands on the arrow keys. One index finger per hand, occasionally using a 2nd finger from one of the hands to reach a certain arrow easier.
Don't limit yourself to a single technique; try a few and get one that works for you.