Pick any easy shape and divide it into sections.
Paint sections in with a few simple colors.
I aim for 3 or 4 main colors to keep the focus on the brush stokes themselves without worrying too much about what sort of picture I'm actually painting.
Have fun practicing a few simple brushstrokes or just lay down a lot of dots to get the feel of your brushes. The harder you press, the larger they will be so practice a light touch and see just how tiny they can get with the same round brush.
