This is a very interesting exercise. Instead of filling as much as possible of the image frame with the subject, make the subject small and have lots of space around it. The matter of fact is, the subject, in this image the leaf, should not count for more 20% of the frame.
In order to blur the background as much as possible use your lens wide open. I shot this image with a prime 50mm lens at f2.8.
Enjoy and create great images!