Wash inside out and rarely. Cotton twill — chinos and casual trousers, shorts, overshirts and unlined jackets — hides dirt well enough that it seldom needs washing after a single wear. Turn it inside out, wash cool with like colours, and you protect both the surface colour and the quiet sheen the weave has when new.
Skip high heat everywhere. A low tumble or a line dry stops twill shrinking and keeps waistbands and hems true. A casual jacket's lining and an overshirt's structure both dislike a hot dryer — pull them out damp, smooth the seams, and let them finish on a hanger so they keep their shape.
Press for smart, leave for casual. Twill trousers take a sharp look from a medium iron down the leg while slightly damp; shorts and overshirts are meant to read relaxed and need little more than a shake out. Steam is the gentlest way to freshen a structured jacket between washes without flattening it.
Brush, air and spot-clean between washes. Most of what lands on cotton twill — dust, a food mark, a splash of mud — lifts with a brush once dry or a damp cloth on the spot, no full wash needed. Treating it this way keeps the colour even and the cloth out of the machine, which is what makes good cotton twill last.