well... kinda wrong forum for this, but for the sake of academics let's delve into it. First of all, what is your car body made of? is it steel or aluminum? or is it fiberglass? That will have an impact to some degree on the correct finishing process.
An important thing to remember in your case is that the paint's bond is only as good as the bond of the layer below it. So if you've got paint chips coming up, i'd question the integrity of your previous paint job.
If it were my car and i were wanting to do it right, i'd start sanding the paint with a much coarser paper. Usually I sand with 220. This removes much more of the old material and provides more "tooth" for following coats to stick to. If the car is steel or aluminum you might just want to get it media blasted so you have fresh metal to work with.
Once you've gotten to your bare surface or as far as you dare go to the substrate, you need to prime correctly. for metal bodies this usually means an etching primer, followed by a primer/surfacer. The etching primer creates an excellent interface between metal and paint. Primer surfacer is the good stuff that sands off like talc powder and gives you that smoothness.
One other thing that's extremely important is surface cleanliness. Always use gloves so your finger oils don't get on the surface, and always use a surface prep cleaner. Use paper towels, and clean the areas you're going to spray next until nothing else is coming away on your towel. Having learned this the hard way, if you've got oil (say, from an air tool) or silicone or any surface contaminants you will quickly discover what a pain in the *** it becomes when your clearcoat starts to fisheye and suddenly you've got to wipe it all off and reapply everything.
So back to finishing, once you've sprayed your primer/surfacer, you really only need to go to 600 grit. A good bc/cc will fill that nicely. So unless you're going under a computer-eye for paint inspection, 600 grit wet sanding is as high as you really need to go for primer. I'm sure you're doing this already but make sure you use a big long sanding block so you don't put any waves into the primer. Wet sanding helps in this way because you can see the way the light reflects off the surface you've created.
when you've got everything properly primed, depending on the level of your technique, you could spray bc/cc and not have to touch the car again. If you do get orange peel (the result of clearcoat sagging slightly on vertical surfaces) you can sand that off with 1200-2000 and buff it back to a shine.
Hope that helps. What color are you thinking about shooting?