rephrased (to avoid copyright) from the '94 vette FSM:
1) park vehicle 25 feet from wall or screen.
2) mark centerline on wall...FSM suggests putting a mark on the center of windshield and rear window and using these marks as a ''gunsight'' for wall centerline (i can think of several more accurate methods, but perhaps this is 'good enuf')
3) measure distance between headlight centers of vehicle and put vertical marks of headlight centerlines on wall equidistant from centerline of vehicle.
4) measure height of headlight centerlines on vehicle (i would use a carpenters level and steel tape to do this) and put horizontal headlight centerline marks on wall.
5) turn on LOW beam of headlamps.
6)adjust headlamps so that the LEFT EDGE (not the center) of the ''high intensity zone'' of the LOW beam is at the vertical centerline wall mark of respective headlight, plus or minus 4 inches.
7) adjust headlamps so TOP EDGE (not center) of low beam, high intensity ball is at the horizontal centerline wall mark, plus or minus 4''.
i (me, my personal method only, not recommended for anyone else) then wait for a night with heavy fog and drive down a straight, flat road to make final adjustment as you can see the beam of light itself, usually 3-4 stops to reset before i'm happy.