Linen is one of the easiest cloths to look after (sample note). Wash it at 30 or 40 °C with a mild liquid, and leave out the fabric softener: it coats the fibres.
Take it out of the machine as soon as the cycle ends, shake it out and dry it on a hanger. Iron it while it is still slightly damp, or leave the creases: they are part of the cloth.
Our washed linen has been washed before it was sewn, so it should not shrink more than one or two centimetres in length.