Hot water opens the fibre, hard spinning twists it, the dryer cooks it. Three habits that age a shirt faster than a whole year of wear.
The basics work: 30°, short cycle, inside out, neutral soap. Dry flat in the shade, iron while still damp. No bleach, ever.
Between wears, hang the garment out to air for a night instead of washing it. Heavy twill and linen improve their drape with time — as long as you give them the time.