Suppose I'll start:
definitely make sure to have a water bottle or some such handy, especially when you're working. I understand that when you're in the middle of something, it can be hard to get up and use a drinking fountain, so if you have a bottle of water next to you it's convenient and you should have no excuse not to drink something when you're thirsty. remember, it only takes a couple hours to become dehydrated, even if you're sitting in an air conditioned room.
if you're working in the shop, or even at the computer, get away from the work every hour or two and take 10-15 minutes to rest. it'll help you keep focused, and it helps reduce the strain on your eyes if you've been working code or web for a while. this can especially be helpful if you've been hitting a dead end and aren't sure where to go.
I'll go ahead and stop there, so other people can have a chance to contribute
