You can find detailed washing instructions on the care label inside your garment.
As a general rule, wash non-wool garments inside out at a low temperature (30 degrees is more than sufficient) and then air dry. Do not use bleaching detergents or fabric softeners.
All wool and knitted garments should be washed in cold water, pulled into shape when damp and dried flat in the air.
Please note that your garment may shrink slightly.