A flawless paint job is mostly prep. Skipping it shows up as bumps, peeling, and patchy colour. Good preparation takes time but makes the actual painting faster and the result far better.
Clean the walls
Dust, grease, and especially kitchen grime stop paint from bonding. Wash walls with a mild cleaner, rinse, and let them dry. In bathrooms and kitchens, watch for mildew and treat it before painting.
Fill and sand
Fill nail holes, dents, and cracks with filler, let it dry, and sand flush. Sand glossy surfaces lightly so new paint can grip. Wipe away sanding dust before painting.
Caulk and prime
Caulk gaps along trim and corners for a crisp finish. Spot-prime patches and stains so they don't telegraph through the finish coat. Now the walls are ready for clean, even paint.