Denim is made out of cotton, and is usually dyed a dark blue. This means that normal washing and drying will wash out some of the dye - and could turn your other clothes blue, too. Be sure to only wash denim together to protect your other clothes.
When washing denim, only use cold water (this will keep most of the dye from running) and use a color-protecting detergent, especially for darker clothes
Drying denim can also fade it, and will make the fabric shrink. Hanging your denim on a clothesline will protect the fabric, but can take forever. If you are short on time, dry your jeans in the dyer until they are just damp, and then hang them outside.
You don't need to wash denim after every use. Spot clean any small stains if needed. To just kill odors, try putting the denim in the freezer, or spraying it with Febreze