A couple of years ago we used to have something called The Graphics School where people could sign up and be tutored (I guess) by more experienced designers.
A teacher would be assigned to a specific group of students based on level of experience and ability. Every week or so you'd be given assignments, you'd complete them, post them and your teacher will give you a c+c on what you did good, what wasn't so good, and what you could do to improve.
Unfortunately, I don't think the school has happened in years. There's really a lack in the amount of people doing graphics currently in this section and most of the people who a good grasp and high level of skill either rarely post here or have left completely.
Sometimes the best thing to do is for yourself to look at a variety of tutorials, make pieces, and ask for some constructive feedback. I might ask at getting the graphics rating thread back in action. Being taught is great, but trying things out yourself and getting feedback from different people can really help you a lot.