Thought of another one: Don't go overboard when buying gifts. If you have to impress someone with the price of a gift, you don't need that person in your life. And vice versa.
If you buy me something for my birthday, I'd much rather have something cheap but personal (eg, a $2 trinket to go on my keychain that will remind me of you/us). Large amounts of cash will always be graciously accepted but not necessary to keep me as a friend.