Here's a couple that have just sprung to mind:
- Never send a cranky/sarcastic email without having walked away from it for at least an hour first. You never know how much trouble you'll get yourself into. Of course, as a general rule - never lose your temper until it's detrimental not to lose it.
- Always check the send to address - autocomplete can do the strangest things if you're not paying attention (oops!)
- Write short, but meaningful emails. Remember that sometimes a very terse email can convey dissatisfaction or dislike. Write to your audience. There are a lot of guides out there suggesting you should write very short emails - that's OK if it's a high volume environment. Not OK if it's a low volume environment.
- Water/Coffee/Coke/Beer + computer = bad. So many combinations that are so nasty in so many ways. Also, try to avoid smoking while computing - it really fouls up your keyboard.