Anyone can tell which wall you did first.

top to bottom, warm water and a little detergent, then a clean-water pass to take the detergent back off. pay attention to the strip above the skirting, the arc around every light switch, and anything within reach of a cooker.

then stop for the night. a wall that feels dry to the back of your hand can still be damp inside, and paint over damp is paint that peels in a year. this is why washing is the night-before job and not the morning-of job.

filler into every nail hole, screw hole and dent, slightly proud of the surface, because it shrinks as it dries. when it's hard, knock it back flush with a fine sanding sponge and feel it with your fingertips rather than looking at it — your hand finds ridges your eye won't until the paint is on.

then get the dust off. a dry brush, then a barely-damp cloth. sanding dust under fresh paint gives you a gritty wall you can feel every time you walk past it for the next decade.

skirting, architrave, window frames, socket plates — tape it, and press the edge down hard with a filling knife or your thumbnail. an unsealed tape edge is a paint tunnel. that's most of the bleed people blame on the tape itself.

the ceiling line is different. taping a ceiling takes an hour, it bleeds anyway because the join between wall and ceiling is never actually straight, and it gives you a line that follows the tape rather than the room. cut it freehand with a brush. it's a five-minute skill and it looks better than tape does on its best day.

an angled sash brush, two or two and a half inches. load it about a third up the bristles and tap it against the inside of the tin rather than dragging it over the rim — a dragged brush comes out half empty and then you press, and pressing is what makes a wobbly line.

lay a band two or three inches wide along the ceiling, down the internal corners, and around the trim. hold the brush at a shallow angle and let the tip do it. and here's the part people get wrong: cut in one wall, then roll that wall before you cut in the next one. cutting in the whole room first feels efficient and it is the single most common way to end up with a picture frame round every wall.

this is the whole reason for the one-wall-at-a-time rule. brushed paint and rolled paint dry to slightly different textures, and if the brushed band has already gone off before the roller reaches it, the two sit side by side forever — that's the picture-frame effect, and it's the thing that makes a room read as amateur from the doorway.

nap depth: three-eighths of an inch for a smooth wall, thicker only if there's real texture to get into. work in sections about three feet wide, roll right up into the wet brushed band so they merge, and don't press — a roller that needs pressure is a roller that needs reloading.

finish each section with one light pass from ceiling to floor, roller barely touching, no reloading. that last pass is what evens out the direction of everything underneath it.

check the tin for its recoat time and respect it. going back in early doesn't speed anything up — it drags the first coat around and leaves a patchy mess that needs a third coat to bury. and while you're waiting: no touch-ups. a brush dabbed onto a half-dry rolled wall leaves a mark with a different sheen that becomes permanent and extremely visible at nine the next morning.

tape comes off while the paint still gives slightly under a fingernail — not soaking, not cured. pull it back on itself at a low angle, slowly. if it's already gone hard, don't yank: score along the edge with a blade first, or you'll take a strip of your new wall off with it.

then wait for morning light before you decide how it went. and if a patch does need fixing, re-roll the entire wall rather than spotting it. sheen doesn't blend.