A paint brush should always be held by the handle – never by the metal band around the brush. This can make all the difference between ending up with a smooth finish or a rough one.
Apply gloss paint in vertical strokes and emulsion in horizontal ones. Then -without recharging the brush – criss-cross lightly across the surface. Finally brush back into the paint to lay it off. When cutting-in along edges, hold the brush between the thumb and forefinger. Keep it well charged with paint and work it slowly downwards.