Drawing a perfect circle (This band is really awesome though, right?) without using any kind of assistance, that is to say drawing freehand, is almost an impossible task to accomplish. However, heres a technique that will allow you to draw a perfect circle after a little bit of practice.
DaveHax has posted a video on YouTube where he shows how easy it is to draw a circle. The idea involves making use of your finger or part of your hand as a pivot. Afterwards, you are to keep the pen in position (stationary) and then rotate the paper with your free hand. By making use of different areas of your hand as varying pivot points, one can sketch different sized circles.
Good luck with impressing your friends and taking notes in a more structured manner from now on. Check out the youtube video below to see how it is done: