Trim gets hit by everything. Vacuums, shoes, dog tails, the edge of the laundry basket. It's also the part of a paint job most people skimp on. This is what has to happen if you want it to still look good in ten years.
1. Clean it
Baseboards are dusty and kitchen trim is greasy. Paint doesn't stick to either. A wash with a degreaser, then a rinse, before anything else.
2. Knock the gloss off
Old trim paint is usually glossy, and new paint slides off gloss. A light sanding gives the new coat something to grab. Skip this and you get the finish that peels in sheets a year later.
3. Fill and caulk
Nail holes get filled and sanded flush. The gap between the trim and the wall gets a bead of paintable caulk, tooled smooth. Not silicone; paint won't stick to it. This is what makes trim look like it was built into the wall instead of nailed onto it.
4. Prime what needs it
Bare wood, filled spots, MDF edges and anything that's been sanded through gets primer. Otherwise those spots drink up the topcoat and show through as dull patches.
5. Use an enamel, not wall paint
This is the big one. Wall paint is made to be flat and forgiving. Trim needs a hard enamel, the kind with urethane or alkyd in it, that cures to a shell you can wipe and bump. On doors and trim where it makes sense, the same two-part 2K approach we use on cabinets gives the hardest finish there is.
6. Spray it if you can
Brush marks on trim look cheap. Where we can mask properly, trim and doors get sprayed. Where we can't, it's a good brush and a light hand.
7. Two coats, and let it cure
Two thin coats beat one thick one. And enamel that feels dry the next day is still soft for a while. Don't tape to it, hang things on it or shove furniture against it for a couple of weeks. We'll give you the numbers for the product we used.
The short version
Clean, sand, fill, caulk, prime, hard enamel, two coats, patience. Every one of those steps is something a rushed painter skips, and every one of them shows up later.