In my personal and professional experience, I would say that learning effective people skills would be on the top of my list. Even if you are very good at what you do, in your personal or professional life, if you are not able to effectively work together with others, you are likely going to have some difficulty becoming a "success". A close second piece of advice would be to take more risks and not be afraid of making mistakes. Although playing it "safe" has its place, taking prudent risks surprisingly may bring about positive changes in your life.
Certified Teacher & Life-Coach