Nothing to prep the surface, just wash it off with car soap. I use the meguiars unigrit sanding discs. They make in all grits. I use 500 800 and 1500 with a Griots 3 inch polisher and the soft pad interface, spraying a small bit of water on them during (called damp sanding). Then wet sand by hand using 2000 and 2500. Then I use a dewalt rotary with a meguiars heavy cut purple wool pad and some of the heaviest compound on the planet, not sold here on AG. Then meguiars m105 compound after that with same pad. Then change to soft foam pad, still with a rotary, and some polish , also not sold here. Honestly, we do 90% auction cars so we dont seal anything, just wax. And the results are always really good. Of course, sometimes you dont need to go as coarse as 500 or 800. But letting the machine do the work is what I prefer.