i smoke cigarettes so i have to wash my shirt at least every 2 wears or i'll smell like an ashtray.
i flip my tshirts inside out and wash them on cold and hang dry. when i hang them up, it pat them down to flatten out any wrinkles then they dry straight.
i hardly ever wash my denim (unless there's some nasty mud/food/jizz stain).
sometimes i let the stains fly though. like i was painting a room once and got some paint on my jeans from when they were sprinkling off the rollers. it left little dots on my jeans, but i thought it looked good. it added some character to my denim.
i wash my dress shirts after every wear to keep them looking fresh, and wash my sweaters every week or so.
i used to get freaked out about washing my clothes too much because they'd get worn out. especially if its a shirt that i really like or something. but then i realized that i can just buy more clothes. there's always something cool out there.