Pickup adjustment is a very approximate adjustment. The following are some general guidelines. Fine tuning of pickup height adjustment should be done to get the particular balance of sound or picking comfort you personally prefer.
Fret the 1st string(high E) at the 22nd fret.
Measure the distance between the top of the bridge pickup and the 1st string. This distance should be approximately 1/16th".
Fret the 6th string(low E) at the 22nd fret.
The distance between the top of the bridge pickup and the bottom of the 6th string should be slightly larger than 1/16th". Adjust this distance by the amount of bass response you like.
You'll probably want the middle pickup slightly further away from the strings than the bridge pickup.
The neck pickup should probably be even slightly further away than the middle pickup