Don, the idea is to dish the wheel so that the rim is centered between the dropouts. The easiest way to do this is to flip the wheel in the truing stand frequently as you're truing it to ensure that as you tension the spokes, the rim remains centered. I have a dishing gauge, but don't use it.

EDIT - Retro Grouch expressed it better; the rim needs to be centered between the locknuts (instead of dropouts).

From Musson's Wheelbuilding