Denim should be worn lots and washed little. The nature of traditional cotton denim is only the outer fibres are dyed and the core of the fibre remains white, everytime you wash a little colour is removed from the outer fibre making the jean lighter and lighter. Over years and continual washing jeans will fade, which is the nature of the fabric. To keep the colour looking fresh for longer wash your jeans as little as possible. To freshen up your jeans you can freeze your denim for 24 hours which will killing the bacteria on the fabric. Spot cleaning only the dirty areas will keep your jeans looking new for longer. When you absolutely have to, wash them inside out on a cool wash, or max 30 degrees is enough to get them clean and remove as little colour as possible. As with all 100% cotton garments heat can cause shrinkage so line dry, out of direct sunlight if possible and do not tumble dry.