One of the problems of photographing close-ups of flowers is that there is usually a lot of clutter around them. You can use sticks and tripod legs and things to try to keep some of this scrub out of the frame, or limit your depth of field to just your subject (use a wide aperture to limit depth of field) so that the background is out of focus, but it's still there. One way to get a nice clean and dramatic look in flower photos is to use a black background. I carry around a big piece of black fabric and also some pieces of black poster board (about a buck a sheet at craft stores). Then when I find a flower I want to isolate, I slip the background in a foot or two behind the flowers (to keep it totally out of focus and with no reflections or bits of white lint showing up).
I used a sheet of back fabric (slung over a lawn chair a few feet behind the flowers) to photograph these bleeding heart flowers in my garden and, just by good fortune, the fabric was in shadow while the flowers were in sunlight. The added contract of sun against shade helps too. I did, however, also use a small amount of fill-in flash because I wanted more depth of field than I was getting and turning on the flash helped me shoot at a smaller aperture (I was working, as always, in the aperture-priority mode) of f/22. Again, because the flash was several feet away from the black fabric (the flash was only about a foot from the flowers), there was no chance of light picking up folds in the fabric, etc. Later in Photoshop I also used the selective color tool to make sure the black was very black.