Check out the Kerrville Quilt guild photos on Sue Garman's website.
http://suegarman.blogspot.com/
Make sure you can come in close some of the details of the quilting is pretty amazing.
One quilting class I had showed how different lines create a peaceful look--horizontal lines-where diagonal lines tend to be more exciting. I think the centers, I would think about horizontal lines, separate to each quadrant. The points maybe a flame type stitch. The outside quadrant circles you could do like the center, or make them like sun rays coming from the center with a s like curve. The outer areas of the points you could do echo stitching, with some type of meander on the outside negative areas. Personally I think it is easier to try to figure out each area, then to just say, make a flame meander throughout.
Try taking a piece of vinyl that you might put over something--it is sold at fabric stores, or even a clear piece of overhead projector sheet and using a vis a vis marker mark how you might do the quilting. If you like it keep it until you quilt it, as a reminder, otherwise windex it off and on to the next idea.