Paint won't bond to greasy or filthy surfaces, like kitchen walls above a stove, mudrooms where kids kick off their muddy boots and scuff the walls, or the areas around light switches that get swatted at with dirty hands. "I always use a degreaser to clean grimy or greasy surfaces," a pro tells PM. "It cuts through almost anything you have on walls for better paint adhesion."
Instead of using white primer, pros usually have it tinted gray or a color that's similar to the finish paint. Tinted primer does a better job of covering the existing paint color than plain primer, so your finish coat will be more vibrant and may require fewer coats. This is especially true with colors like red or orange, which could require three or more coats without a primer.