Use less detergent. Most detergents today are highly concentrated and can be used sparingly. Too much will build up on the fibers of the laundry and cause stiffness.
Add vinegar to the fabric softener dispenser. Vinegar is a natural fabric softener that can strip soap buildup.
Shake out wrinkles before hanging on the line. This replaces some of the tumbling action of a dryer and prevents wrinkles.
Avoid hanging the laundry in full sun or at the hottest time of day. The longer it takes to dry, the softer the laundry will be.
Hang laundry on windy days and the wind will move the laundry so it doesn't get stiff as it dries.
Bring the laundry in while it is slightly damp and finish drying in the dryer for 10 minutes. This still saves energy, but softens the fabrics.