A friend of mine who restored a VW Bus a while back gave me some great advice on painting. Basically, you lay down a coat of heavy build primer that is colored Buff, then lay down black over that. This way, as you're sanding, you know when you've sanded too far, or it becomes visibly apparent where you need to build up more. It's basically a really handy way to reveal all of the areas of your car that you need to pay more attention to.
Which makes a ton of sense. As it stood, my car was a mixture of various shades of black, tan and green. This made it really hard to tell if I had smoothed out the rough spots.
Here are some pics of the first pass of Buff paint I did to the car. My main focus was on the side, obviously, and the seam that ran down it.
Overall, I'm SUPER happy with how clean things are. Still plenty of work to go, but I can see now that I've really made quite a difference in the body. The seams are cleaned up pretty well, the gas cap is completely smoothed out... overall really great.
From this picture you can really see how the paint exposes areas that need work. I knew going in that this part was a rough spot, but I find it really interesting how the paint reveals the areas that need work.