Very interesting, horribly broad topic.
In my experience, my greatest developments have come from two things:
1. Constantly pushing myself just beyond my comfort zone.
2. Failing
Although, the latter took me a long time to realize.
#1
I think that many people think that they are improving, when what they are really doing is just not getting worse. There's an easy contentment that comes from operating only in realms that you excel in. This is compounded, I think, by the fact that we really aren't aware of all of our shortcomings, even some of our bigger ones, which makes it hard to focus on fixing them.
Many of us like to focus on what we are good at and get better at it. It's nice, because you never really have to push yourself too hard and you can stay in relative confidence and maintain the self-esteem bubble, but it's only a temporary fix...and it doesn't bring us to our full potential. You really have to learn and experience everything you possibly can. It's amazing the ways in which things are connected that you would never expect. Many times the knowledge or insight that we need to take a skill to the next level is found in a completely unrelated field.
The best way to consciously improve, for me, is to regularly push myself just past my comfort zone. If you go to far, you lose confidence because of major failure. If you don't go far enough, you may still gain some skill, but not much. If you go just past your comfort zone, every time, not only do you gain skill and experience, but you gain confidence.
#2
Reminds me of the last poem on this post
It took me a long time to realize this, but I think that all of my greatest developments have come from times that I've failed or lost. Part of this is my competitive drive that forced me to work harder, but a greater part of it is the way that it forced me to view things differently. It also made me realize the limitations I had at the time and helped me understand that I'm not just naturally good at everything and I don't just deserve to be successful at everything. It takes constant effort. If you think you are just naturally awesome at something and you don't need to work hard, then you just haven't met anyone else that's good at it or you aren't pushing yourself hard enough.
You really have to be confident enough to admit vulnerabilities and weaknesses. Think about why you do everything the way you do it and how. Question your own motives, not just other people's and don't just set goals. Create a vision of the future and then find a way.
That's my take, anyways.