Read the care instructions (usually contained on the label of the fleece garment) before attempting to wash it.
Zip up any zippers on the garment to prevent loose zippers from catching on the fleece as it washes.
Turn the garment inside out to prevent pilling. Pilling is the development of small balls of fleece on the surface of the fleece and does not reduce the effectiveness of the garment but can look unattractive.
Turn your washing machine settings to cold water and gentle cycle.
Add a mild detergent. Do not use products that contain bleach and avoid fabric softeners. You can purchase fleece-specific laundry soaps from Columbia and other sporting goods stores but a mild detergent is usually gentle enough.
Wash the garment separately or with other fleece items of a similar color.
Hang the garment to air-dry. If you absolutely must use a dryer, use the air tumble setting. Air-drying reduces that chance of the garment forming piling.