To extend the life of your quilt I recommend you spot clean with warm water and mild soap when needed and before storage. It also helps to air out your quilt. I do this outside on a warm/sunny day. Lay it flat on a clean sheet with a clean sheet over it to avoid fading.
When you do need to wash quilts my first recommendation is hand washing and then lying flat to dry. I know this is not always practical so if you choose to machine wash use a large, front loading,
non-agitating washer on gentle cycle with mild soap. Home washers with an agitation arm are too small and the agitation and spinning will cause damage.
Lay the damp quilt flat on a clean sheet to dry. This reduces stress on the quilt. Drying in a dryer is an option but puts more stress/agitation on the quilt.
Do not dry clean. As a quilt historian I stand firm on no dry cleaning. The chemicals used can build up over time and cause damage.