Like everyone else, I love circles!
Even the prehistoric civilization loved them (see Stonehenge).
If you look in nature, you will find loads of circles as well.
I've been drawing small forms of sea life here lately, which (no surprise here) contain circles!
These circles are quite simple , easy to draw and addictive.
If you take them down to the most simple form - they are circles with legs (on the left)
and a line of (elongated) circles on the right.
I've added loose lines around the outline to make the shapes seem more fluid.
I've made thermofax screens out of one of the sketches that I drew of similar sea life.
If you're having trouble drawing things with circles (or just want to look at more), try looking on Google for "circles in nature".
I clicked "images" on the Google search to get the above results.
Hope that you are enjoying your sketchbook time!