Loosen One Side
To dish a wheel start by loosening all the spokes on the side you want the rim to move away from. Loosen the spokes by turning the nipples clockwise to screw them along the spoke away from the hub. Start at the valve and work round turning each one going to that side of the hub by a set amount, half a turn is a good starting point.
Check the dish of the wheel
Check how central the rim is. This will tell you how far the rim has moved and how far to turn the spokes in the next round of adjustments.
Stress The Spokes
Between each round of adjustment and re-diagnosis stress the spokes using the procedure checking spoke tension and squeezing hard. This releases any twisting forces trapped in the spokes as you dish the wheel. If you don’t do this the forces will be released the first time the bike is ridden and the wheel may go out of true straight away. This stressing process is the main difference between a hand-built wheel and one built by a machine.
Repeat the steps to dish a wheel. On a bike for general use a few millimetres out is acceptable, though not ideal.
Check the spoke tension, and the rim truth and correct as necessary.