I want to take my car to one of those quicky paint job places. But i’d like to do my own prep work. I’m not sure which grade of sandpaper I’d should start with and end with. Anyone have any suggestions? Help would be appreciated, thanx.
This might merit GQ, but I’d check with an auto body shop first anyway. Unless you have a POS car, then just rub it with a brick. 
Whatever you start with, you want to finish up by wet sanding with 600 grit, and all scratches etc, nicely feathered.
Man, I’ve done that myself, and it is not worth your time or effort. Good luck, if you do try to pursue it. You may want to invest in an orbital sander. Don’t use a circular sander – using that on an auto body is like playing the violin - you can’t just pick it up and do worth a darn with it. Call around some car parts/paint places and get some advice from those guys. Don’t call a car parts supermarket, though. Look it up on the web. I bought a auto painting book that helped me out a lot (got it at a parts store).