For outdoor flowers, try to shoot on an overcast day or during golden hours of morning to get that really diffused light.
Another thing in shooting flowers is to have your settings correct, actually digital cameras have made it simple these days by giving us the little flower icon, which is also the macro setting. When you are close to the flower, with macro setting you will be able to get sharper images with details.
In a nutshell, for a better photograph of a flower, use natural lighting, macro lens setting and an angle to fill the frame to the frame by the subject.
Inset picture shows a cactus flower with a close-up to almost fill the frame with yellow flower and green background.