Laundry-care guides recommend cold washes, flat drying and reading the label, as if a label has ever been read before the damage was done.
Plan for the shrinkage. Buy every jumper two sizes up and let the machine tailor it down over the season. WARNING: the certification board rates this dangerously close to useful — there is, in theory, one wash where it fits. Field notes put that wash at number seven, give or take four, with no notice: before it you wear a tent, after it, a vest.