Wash your clothes in cold water using cold-water detergents whenever possible.
Wash and dry full loads. If you are washing a small load, use the appropriate water-level setting.
Dry towels and heavier cottons in a separate load from lighter-weight clothes.
Don't over-dry your clothes. If your machine has a moisture sensor, use it.
Clean the lint screen in the dryer after every load to improve air circulation and prevent fire hazards.
Periodically, use the long nozzle tip on your vacuum cleaner to remove the lint that collects below the lint screen in the lint screen slot of your clothes dryer.
Use the cool-down cycle to allow the clothes to finish drying with the heat remaining in the dryer.
Periodically inspect your dryer vent to ensure it is not blocked. This will save energy and may prevent a fire. Manufacturers recommend using rigid venting material -- not plastic vents that may collapse and cause blockages.
Consider air-drying clothes on clothes lines or drying racks. Air drying is recommended by clothing manufacturers for some fabrics.
If you have a front-loading washer or high-efficiency top-loader, use detergent labeled for high-efficiency (HE) machines. According to the American Cleaning Institute (PDF), HE detergents are low-sudsing and quick-dispersing to clean well in high-efficiency washers that use less water.