The one rule that matters most: no bio detergent. Silk is a protein fibre, and the enzymes in biological or 'bio' detergents are made to digest protein — they cannot tell a stain from the fabric itself and quietly eat away at the fibre, showing up as thinning or small holes after a few washes. Use a pH-neutral, enzyme-free delicate or silk wash only, and skip bleach, optical brighteners and fabric softener entirely.
Wash cool and gentle. Hand washing is safest, in cool to tepid water below 30°C — hot water tightens and shrinks the fibres. If you machine wash, turn the piece inside out, use a mesh bag and a delicate cycle with little or no spin. Wash it alone or with like-coloured delicates, and don't leave it soaking longer than about half an hour.
Squeeze, never wring, and dry in the shade. Press the water out gently, roll the piece in a towel to blot it, then dry it flat on a rack away from direct sun and heat. Wringing and tumble drying both distort and weaken wet silk, so avoid them completely.
Iron cool, or steam. Press on a low, cool setting while the silk is still slightly damp and inside out, or lift creases with a hand steamer. Store in a breathable cotton bag rather than sealed plastic, which traps moisture and can yellow the fibres over time.