You can trace a circle around a lot of things.
You could trace around a can of coke, a burger king cup, a regular cup, a bottle of water, a water bottle cap, a roll of duct tape (inner or outer ring) a paper towel/toilet paper tube, or a mood ring...
And, if you have a compass, you can make circles with that.
I recommend using a compass, just like hectictar said. If you don't have own, practice drawing circles by moving the pencil around one point on a paper. If that still doesn't work, hold down the pencil on a part of a paper, preferrably the middle, at an angle. Then, turn the paper around either clockwise or counterclockwise. Just don't hold the pencil at a big angle or the circle will be too big. Good luck!