This one doesn't really apply to me and I'll explain why in a second, but...
* Don't be afraid of your guitar.
I've always been a tinkerer, and even going back to when I was 12 years old and got my first
electric guitar, my dad and I took it apart to see how it worked. I was never scared to tweak it or change my guitar to make it play and sound better. But I've met guys who are terrified of their own guitars - people who are frightened to bend a string too far, or to go wild on the whammy bar, or who cradle the pickup selector with a look of absolute panic, like if they're too rough with it the entire guitar will fall apart in their hands, and whose playing sounds timid and weak as a result. You serve your music better if you are able to forget about worrying about your guitar.