I prefer to learn from other people's mistakes. If you have to learn from your own mistakes where denim is concerned, then it's usually an expensive lesson, like asking your mom to do your washing and she uses a washing powder that includes bleach. It's the same when taking your jeans to the dry cleaner and the tailor, make sure they love denim as much as you do, before handing over your precious cargo.
I've just joined another denim and fashion related website called Style Forum.net and there I read about this poor guy called h4zin, who took his raw denim jeans to the local dry cleaner. "So, I took my pair of New Standards to the local oriental dry cleaners to get it hemmed. Bad move I know. I made sure to say "DON'T WASH IT" like 5 times... but I did not even think that they would iron/press the thing. Luckily it only had about 10-15 days of moderate use... but it sucks to see my work all gone. And guess what... they PLEATED IT in the front, as if it were a pair of dress pants. What kind of moron puts front pleats on jeans?! Unbelievable. So now I had to take it back so they can press it again to get rid of that."
It's a very funny and sad story at the same time, but you need to remember that there are others out there, who really don't know that much, or anything for that matter, about denim and frankly don't care. Always make sure you ask people who know, to clean your jeans.
Here's another lesson I learnt from someone else's mistake, about spinning jeans in the washing machine: "I spun my Samurai s500wx just to get the water off (no heat) and regretted it. After 10 mins, I checked on my baby and found a murder scene in the machine. It was blue everywhere. Don't do it."