Drawing some designs all over pieces of paper, before you sew them, can help. Be sure you pull up enough slack around the area you are quilting so that you won't be pulling on the quilt while trying to make your circular movements. That can make jerky curves.
A charity quilt is a great thing to practice on because you are learing how to handle a big quilt, and also providing something warm and cozy to the recipient. It doesn't have to be perfect. And remember you can always pick out the ugly parts and re-do them. You will get better, so don't get discouraged. (Preaching to myself here, too!)