Light Stalking has an interesting twist for offering advice to photographers — things you shouldn't do rather than things you should do. Three of my favorites are “Don’t be afraid to ask for help”, “Don’t assume your way is the best way”, and “Don’t ever stop learning”.
I guess if I could add one point to the list, I would say “Don't be so serious”. Photography is fun, interesting, and exciting. Most of us got into it because of one or more of those reasons. If you've turned into the cynical job-hating photographer always wearing your grumpy face, why are you still shooting?
Any other tips for things that photographers shouldn't do?