Prep is 80% of a good paint job, mate. Get it right and the topcoat practically applies itself. Here's the order that matters.
Clean. Walls collect grease, nicotine, dust and the odd handprint, especially in kitchens and hallways. Wash with sugar soap, rinse with clean water, let it dry fully. Paint won't grip a dirty wall — that's where peeling starts.
Fill. Knock out cracks and dents with a decent filler (Toupret and Easifill are the trade standards). Overfill slightly so you can sand back flush — fillers shrink as they dry.
Sand. Once cured, sand filled areas smooth and give the whole wall a light key with 120–180 grit. This knocks the nibs off old paint and gives the new coat something to bite into.
Prime where needed. Bare plaster needs a mist coat — your topcoat watered down 20–30% — before full coats. New filler patches and any stains (water marks, biro, damp) need spot-priming or they'll grin through. Zinsser BIN is the gun for stains and tannins; Cover Stain for trickier surfaces. Don't skip this — a stain will bleed through three coats of finish paint and you'll be furious.
Dust off. Wipe down with a slightly damp cloth or tack cloth so you're not painting sanding dust into the finish.
The most common cry I hear: *"do I really need to mist coat new plaster?"* Yes. Fresh plaster is thirsty and alkaline — paint it neat and it'll flash, peel or never fully cure. A thinned first coat soaks in and seals it.
Once you're properly prepped, almost any quality emulsion will sing. Little Greene Intelligent Matt, Farrow & Ball Estate Emulsion in something like Pointing or Cornforth White, or COAT if you want a hard-wearing, low-VOC option in a tone like Earl — all reward good prep with a flat, even finish.
Practical tip: do all your filling and sanding in one session, prime the patches, then leave it overnight before topcoating. Rushing wet filler or fresh primer is the fastest way to ruin the finish you've worked for.