Da Rock said it in his post, but I believe there is one point that needs some consideration here.

All initial settings should be set to the center of the surface throw. Let's use the Elevator as an object point.

Center the elevator and immobilize it somehow. I use two lengths of 1/8th ply about four inches long by two inches wide. I 'sandwich' the elevator between the ply, securing the ply with two lite clamps (See picture). This secures or immobilizes the elevator to the horizontal stab. This assumes that the horizontal stab is NOT an airfoil shape. Many, if not most, of our trainers or second planes use a flat surfact on the top and bottom of the horizontal and vertical stabs, so this will work. This also centers the elevator to the center of the airflow over and under the horizontal stab.

The next thing I do is center the servo and make sure the trim tabs on the transmitter are in the center. Keep the transmitter and receiver on. This will insure that the servo does not ove during this adjustment. This is easy with the DX7 because the display screen is easy to see and shows where the trims are. Enough commercialization here.. If you use a fresh, reset model on your computerized radio you should be ready to go.

The next thing to do is to connect the control rods to the servos but not to the control surface horns.

Next is to adjust the clevis to the center of the hole you are going to use. (See Ken's and Da Rock's drawings).

Then connect the clevis to the horn, making sure that the connection does not try to move the elevator. If it does, then make the necessary turn adjustments on the clevis until it does not move the surface, and connect the clevis to the horn.

Then carefully and slowly remove the clamp(s if you used two or more). The elevator SHOULD NOT MOVE. If it does move, then investigate why and fix that problem. Remember, you secured the elevator with the clamps and adjusted the clevis to the center of the desired hole on the horn. If the elevator moved, then it is an adjustment issue.

Once this is done correctly, the surface is centered. This will work to some extent with all of the other surfaces. The aileron on flat bottom wings is easy to do, just remember that you are making the alignment to the flat, or bottom surface. On symetrical wings, well, use your imagination and ingenuity, but by the time you are ready to fly a fully symetrical airfoil, you should be well beyond this basic adjustment procedure.

If done correctly, and if you built the aircraft correctly AND straight, it should require a minimum of trim to fly straight and level.