The Meguiar's three-step system is by far the best out there, IMO... Sure, it's a pain in the ass to apply (and de-apply!) three coats, but when you're done - it really, really looks hot.

If you're changing brands or have scratches and want to really clean up the paint - wash the truck down in dishwashing soap, which will remove all the wax. Start fresh, start clean.

Remember - whatever wax you use, apply front-to-back only, never in circles. Remove only with a clean cotton terry cloth (freshly washed, no softener, rip label off). Don't do it in the sun. Always wash the truck before waxing!