A good interior paint job is about ninety percent preparation. The rolling is the fast, satisfying part; everything that makes it look professional happens before the lid comes off.
Protection comes first: floors covered edge to edge, furniture moved or wrapped, outlets and fixtures removed or masked. Then the walls get inspected in raking light, which shows every nail pop, dent, and old patch that flat overhead lighting hides.
Repairs follow. Holes filled and sanded flush, cracks taped rather than just filled, gaps between trim and wall caulked, and glossy trim scuff-sanded so new paint bonds. Every repair gets primed, because patch compound absorbs paint differently than the wall around it and will flash through a finish coat otherwise.
Only then does the paint go on: cut lines by brush, walls rolled in consistent passes, two coats for a true color change. If a painter's estimate doesn't mention patching, sanding, caulking, and primer, ask where that work went. It's usually the first thing cut to lower the price.