So I know I myself don't know the proper way to wash my jeans to keep the color from fading, but Underground Clothing has a few simple instructions to keep your jeans looking new for as long as possible:
1. Read the manufacturer's care label. If the directions for washing differ from below, always follow the instructions on the tag.
2. Empty the pockets of your jeans, do up all buttons or zippers and turn your jeans inside out.
3. Set the washer to delicate, using the cold water setting (cold water & rinse).
4. Add mild detergent (never bleach) and always wash jeans with other jeans. When detergent is dissolved, add the jeans, and start the cycle.
5. Wash light and dark jeans separately. Dark/black jeans tend to shrink and fade faster than lighter jeans.
6. Try adding some vinegar or regular table salt to the wash water (about 1/4 cup) to minimize fading.
7. When the wash cycle is complete, remove your jeans promptly.
8. Turn the jeans right side out and hang them by the waist on a pant hanger. Never put your jeans in the dryer as it can cause irreversible damage to the fabric and color.
9. When dry, hang your jeans rather than fold them to avoid wrinkles and creases.
I hope this helps! It sure helped me =)