Emphasize the flower's center & blur the rest as much as possible. Put the center off-center for a more interesting composition.
The Nikkor-micro 105 is an f/2.8 lens, but don't count on f/2.8 in all situations. It's only f/2.8 at a focus distance of 10 feet or longer (at which point it's no longer a 1:1 macro or even close to it). In fact, slap a 1.4x teleconverter on it and get in as close as possible (where it is, in fact, 1:1) and the best that you can do is f/5. The f/4.8 on this shot is wide open (probably about 1.1:1 without the TC and larger than life size with it).