Weight in the rear. As little weight forward as possible. 3 wheels touching (obviously, have the high one be forward, as the weight is in the rear). Extend the wheel base - don't use the factory notches, pull those wheels out even with the ends of the block (don't go over - generally race officials have a box that the car has to fit in. If it doesn't fit, DQ).

Go to a hobby store and get a wheel turning mandrel. Chuck it up in the drill press, and go to work on the wheels. Most rules don't allow narrow wheels, but you can get the same effect by slightly working the wheels. Narrow the point of contact as much as possible, but giving the center of the wheel an ever so slight crown. Wax the wheels, remove all the casting imperfections from the wear surface (especially the inner hub face).

Chuck the axles in the drill press. Clear the casting burs on them (they are generally horrible).

If you can check the track ahead of time, get the launch pin height. Have the car touch the top of the pin, not the bottom, as in the time it takes to tip the pin down, the top of the pin has traveled further.

Aerodynamics do play some effect, but not as much as one might imagine. We've often placed fairly well in the speed category with some cars that were exceptional in the creativity department (basically, a rolling diorama with some sort of pun played in).