The last of five suggestions in a Fast Company post titled "Five Things to Do Every Day for Success":
Write a handwritten note to someone. Seriously. It is a lost art and makes quite an impression. There is always someone you can send a thank you note to--or you aren't doing things correctly.
Though the other suggestions are good ones, too, this one really resonates with me. I've been in awe of the power of handwritten notes longer than I can remember.