The secret to knowing how to wash sweaters depends on the material they are made from. Carefully read the label to see the material the sweater is made from as well as the recommended care instructions. You are always free to wash your sweater in a gentler method than the one suggested on the tag, but you should avoid using methods harsher than the ones listed on the tag.
If your sweater is made of a sturdy synthetic material or wool, it is probably okay to machine wash and machine dry it. However, sweaters made of more delicate materials might require hand washing before being laid flat to dry. For water-sensitive materials such as wool, dry cleaning or steam cleaning would be the most suitable cleaning method.