Ask any experienced painter where a good paint job comes from, and the answer is the same: prep. Expensive paint rolled over a dusty, patched, glossy wall will still look uneven and start failing early.
Good interior prep starts with moving and covering furniture and floors. Then every nail hole, crack, and dent gets filled and sanded smooth. Gaps along trim and baseboards get caulked so the finished line looks crisp.
Stains from water, smoke, or markers need a stain-blocking primer, or they will bleed through the new color. Glossy trim needs light sanding so the new coat can grip.
Only then do the finish coats go on: edges cut by hand, walls rolled evenly, and enough drying time between coats. It takes longer, but the result looks professional years later instead of months.