On the wall or garage door mark the lights' horizontal centerlines with masking tape. This masking tape thus should make a straight line across the wall. Also mark the vertical centerline for each light. So you should now a basic idea or T area where the headlight should be centered.
Next move your car back 10 to 25 feet from the garage or wall. Before turning on your lights, find the adjusting screws. These screws typically will be inset close to the headlight. You will want to find these screws ahead of time instead of searching for them after the headlights have heated them up and they are too warm to touch.
The adjusting screws should consist of a horizontal screw and a vertical screw, each with a small spring behind it. Some higher end vehicles come equipped with a small level. If your vehicle has this you will see it attached to the top of the headlight under the hood.
Now turn on the headlights on the low beam setting. When you adjust the low beams, your high beams should set to the right level as well. With the lights now on, see how the beam matches up with the horizontal and vertical masking tape lines you have placed on the wall.
Turn the adjusting screws slowly with the screwdriver while watching the light beams on the wall. Turning the top adjusting screws clockwise should raise the beam while turning them counterclockwise should lower the light beam.You adjust the lights to the left or right by turning the side adjuster screw.
You want to adjust the low beam lights so that they hit two to four inches below the horizontal centerline and two to four inches right of the vertical centerline. You do not want the lights to be completely centered either horizontal or vertically. If the lights were totally centered they could blind the oncoming traffic when you drive on the roadways. Being pointed slightly down from center allows the light beam to keep light on the road.
Once you have turned the screws and aimed the light beams accordingly, your headlights should now be properly adjusted. You can rip off the masking tape and throw it away, put away your screwdriver and pull you car back into the garage. The 15 minutes you used to adjust will now allow you to drive better in the dark.
If you're maintaining an older car, you may be wondering about how it insure it as well. See "When to drop comp and collision" and "Insure your car from showroom to junkyard." Correctly aimed headlights won't earn you a break on your rates by themselves, but an accident- and ticket-free record is crucial to getting a good driver discount.
Remember that cars can differ, so check your vehicle's owners manual if this technique does not work for your car. Also see how often the manual says you should check the headlights and they should be adjusted. Normally it is recommended that headlights be adjusted every 12 months or whenever you notice that the lights are out of alignment.