All designers know how to improve their designs. They read, they study, and they attend workshops. Articulating failures and successes and the reasons for each is also a great way of pushing something forward. Improving each and every time is a sure fire way of creating a successful design.
One topic I think does not get enough exposure is how to sell your ideas properly. I wrote an article for UXmag about this topic. I tried to give as much advice as I could to help. When I was first faced with the challenge of trying to present good ideas, I was taken aback by how no one else could see it. To me it was so obvious.
A few years ago I was approached by Bestica, a UX Company, with a question. They wanted to know what advice I would give to UX Designers in improving their careers. The advice that I gave was about selling your ideas of course. Being an advocate for good design as well as your own is a great way of moving yourself to the next level. Here is that interview.