Preparing for paint
I'm working on a painted cabinet. I'm planning on putting down 3 to 5 coats of paint on the cabinet. Do I sand after each coat, or only after the last coat has been laid down?
The first coat of a painted finish should be primer, which has a high solids content and sticks to raw wood better than paint does. That primer coat may raise the grain a bit, so sand after. This is also the time when you'll see any little defects in the surface that should be filled to provide a smooth substrate for the final paint. Fill the holes, re-prime those areas, and sand smooth.
Paint, following the instructions on the can. Oil-based paints are essentially pigments suspended in varnish. If you're putting on new coats as soon as possible, the coat below will still be chemically active and you don't need to sand to achieve adhesion. If you've waited several days between coats, you probably need to scuff sand.
Water-based paints have a slight tendency to melt into the previous layers, so it's less important to sand them between coats. In either case, however, sand if you need to remove dust, bug parts, brush hairs, or anything else that dried into the paint layer. You probably don't want to sand after the final coat unless you're trying to change the sheen. A good way to get an almost perfect final coat is to let the previous coat dry well, sand it smooth and clean off all sanding dust, then apply the final coat with a little extra thinner so it goes on thin and has time to level before drying. Protect it from dust as it dries.