Nowhere is practice a more visibly component of skill building than here. I've heard some potters say it takes two to four years to master the skills. Others put it terms of volume, such as the potters who suggest that you need to throw over 6,000 pounds of clay before your skills are honed.
Practice, Practice, Practice
The primary component to building throwing skills, as you probably have guessed, is practice. The more time you spend actually throwing, the faster your skills will improve. Practice enables us to unite our minds, our bodies, and our clay as we bring them all to work together toward the goal of the well-thrown pot.
To better understand this, as well as for pure enjoyment, read A Potter's Tale of Practice.
Evaluation of our work is a critical part of each of us building our skills and vision both as a craftsman and as an artist. One of the best ways I know to build your ability to evaluate your work objectively is to take classes that include the critiquing process, such as at a college.
When working on your own, I suggest sitting down for a day's throwing with the goal of dissecting each pot you make. After you finish each pot, cut down through it and examine it for wall thickness, floor thickness, and lack of blebs. Consciously consider the kinetic feel of the throw you just made with the visual information you are now getting. This will help you develop and hone your skills at the wheel.