Micro quilting circles is a great filler for quilt blocks.  Micro quilting circles are small circles touching each other and continuing around  until the block is full.  You can micro quilt circles on your regular sewing machine by dropping the feed dogs and moving the fabric in small circles.  Or on a long arm machine in free motion moving the machine around the fabric.   A great way to learn micro quilting is by practicing making circles with your machine in free motion on a 12×12 sandwiched with fabric, batting and backing until you feel comfortable to tackle your quilt top.  Try different types of batting to see what look you like.

Check Video tab for the demonstration.