Don't let people with terrible hair cuts cut your hair. If they are supposed to be the experts, and they have bad hair, run. I don't mean "edgy, but you couldn't pull it off" -type hair. That is revolutionary, and you should get a hair cut immediately.
Don't surround yourself with problem-oriented people when you need a solution. This is such a tough force, at work in particular. Instead of hearing all of the ways that you can't, find people who can help you find the one way that it can be done. Thomas Edison once said, "I didn't fail. I just found 2,000 ways how not to make a light bulb; I only needed to find one way to make it work."
Don't save things that you could be using or doing today. I remember how I used to save things, like my favorite candle. I would never burn it, saving it for some special occasion only to find that it melted in storage anyway. Wear the shoes you are saving, burn the candle, use the expensive hair product. The small treasures are what make them worth having in the first place.
Don't waste your time being upset at others. Have a friend that wasn't a friend to you? Instead of being upset towards them, either forgive them or simply decide not to be around them. See a stranger who is a total jerk to you? Imagine that they must have a tough life if they have to be mean to a total stranger, and have gratitude that you don't have to live that way.
Don't stop believin'. Journey is never wrong.