well here are some things i learned from trying to paint my car myself
1 do it in a garage if u can, prepping and painting
2 dont use your hands to sand the car or a square palm sander
i used some type of sanding block that was made out of material like a sponge that didnt leave any finger grooves/ and or a long sanding block for the door panels and such
3 u can sand with a rougher grit than u would think, the first time i used 180 for the pre primer sanding and it took forever. u can safely use 80 grit and just spray filler primer
4 and lastly take as many panels and fenders and such off and paint them separately, but at the same time as when u paint the car
hope some of this helps