Woody is correct, prep is the key. I can't tell you how many times I've seen people start sanding without giving the area to be painted a good cleaning first. That includes using a wax and grease remover FIRST. If a surface has any wax residue on it when sanded, the wax can be driven into the sand scratches where a subsequent degrease will not remove it. Then you get your fisheyes. If you are getting fisheyes of a regular basis you either aren't cleaning it correctly or the surface you're painting over has FI eliminator in it.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.