1. Use a dry lube such as graphite, or white Teflon only. Oil damages the paint, collects dust, and may damage the track. Cars found to be using liquid lubes will be disqualified.
2. Break in the wheels by spinning them with lots of graphite. 
3. Right before check-in, fill the wheels wells with graphite.
4. Put a small drop of white glue where the axle goes into the car body and put powdered graphite on it there. That causes less friction if the wheel should rub against the car body.
5. Other than the good polishing of the axles, dump the axles and wheels in a Ziploc bag with some graphite and shake them for a few days prior to the race. That way the wheel and the axles are as slick as can be.