1. Axles must be in straight front to back. That is square to the body. True the axles, don't trust the slots! If you have one, use a drill press to ensure all axles are straight. One of the front and two of the back should be measured to be the same height.
2. After pressing in the axles, test the car for crooked wheels...roll it on the floor. If the wheels are on straight, the car should roll 8-10 feet in a fairly straight line. Should the car turn left or right, you need to tinker with the axle placement without removing them from the car body, until it rolls straight.
3. Do not put the axles in at the top of the groove. Put them in at the middle. This lifts the car off the track a bit more and reduces the chance of rubbing on the center strip.
4. Glue the axles in place. Nothing is worse than having the wheel fall off as you cross the finish line.
5. Once you match a wheel and axle together with graphite, keep them together. They wear into each other as a matched set.