Most paint failures come from rushed prep, not bad paint.
Cleaning and repairs
Walls are washed, cracks are filled and loose paint is scraped and sanded smooth.
Protection
Floors, furniture and plants are covered before a brush comes out.
Good prep is the difference between a five-year and a fifteen-year paint job.
Primer where it matters
Bare wood, patches and stains get primer so the finish coat looks even.