[Atmosphere]

I personally like using 2000 grit as it gives you extra control over the surface. Usually once you find the tint the sandpaper will be nearby.

Sand the tails initially to help the first coat adhere, then lightly sand again every two coats thereafter. Once you've gotten to your desired darkness and the tint is throughly dry (it's usually pretty dry after an hour, but wait a good 12-24 hours just to be safe) sand again and apply your clear coat. You shouldn't need any additional sanding after the clear.

Also, and this is a big one: make sure you spray the tint from all directions (or at least alternate directions between coats), other wise you'll end up with light areas around the edges.

If you mess up, rubbing alcohol or gasoline (whichever is more plentiful) will remove the tint very easily.