There are two ways that I have found most effective. The first is drawing with your arm rotating at the elbow, instead of drawing with your wrist, then cleaning up any mistakes afterwards. The second way is investing in a circle template, it has a wide range of different circle sizes and their measurements on it.
This reminds me of the times I had to do it freehand. The elbow technique works, but I would say that a very effective way is to make a square, make four quadrants in the square like a window, and carefully sketch out the circle as if you are doing it in parts. It helps you understand symmetry