Primer And Sanding Help

I am finally picking up a good parts car and was wondering how would I go about sanding some of the paint. The parts car is white (origanlly blue, same as mine), I think it was spray canned. I need the rear hatch and wanted to primer it black and was wondering how hard this was. The white paint is rough, and I don't know what grit to sand with and how to sand it (worked on rc cars, does this count?), but I can learn. Also I got a brand new 77 280Z hood that is primered gray i think. It is gray and smooth on both the inside and out. was wondering if the part need to be sanded and then primered or just primered. Whats also the typical process of primer? For example; Sanding, Primer, Sand or is it different? :ninja: I will be using Dupli-Color sandable black primer SPRAY CAN. any help on this would be great. thanks for all the help:ninja: