Though in more general terms -
It's important to study theory and put that into practice. I often find that books on theory just confirm what I've already been taught by other performers, though I do enjoy reading it anyway.
It's very important to have a few people who will not just constantly tell you that you did great. That will not help you. You need to find people you trust who will be honest about what worked and what didn't, and what their impressions were. Often times you will find that what you are trying to do is not coming through to the audience. People who are experienced can help you find those miscommunications and fix them.
For me I have a few friends who I trust. I periodically ask them for their opinion, usually over drinks to take the sting out, and then I consider what they say and fix as necessary.
Another point of thought: When someone gives you critical feedback, you don't have to listen to their exact words, but you should look where they are pointing things out to see if something is out of whack.