CIRCLES!

You can use lines but that'll take time. This is what I made up, go to the sketch layer at the bottom right and use the airbrush tool to make a formal circle. Go to your other layer and try to trace over it by a pen, your sketch layer does not show up when finished though. 

If you think that's hard, then go to the sketch's layer and create four lines like this

-trust me. It helps. Then go to the drawing layer and create a perfect circle! *well humans can't draw perfect circles but whatever lol*

AND the third option, use a tablet :D.