For good focus, move the camera forward or backward slowly to get a clear focus. Take your time in focusing and composing your flower, using the full frame of your camera. A tripod or a firm rest for the camera will prevent shaking of camera and blurring of the image. Consider placing a piece of black colour cardboard for the flower to stand out.
You may try two options for large size flowers, first, a wide open aperture setting of f/2.8 or f/4 and focus on just one small area of interest. Look for contrasting colors, patterns and textures for this. Use the timer delay in order to prevent movement in the camera. As a second option, have smaller apertures and a spray bottle to mist the flowers with water or wait for an insect to visit the flower for added highlights. One needs to be patience. In other words, you must experiment to get different compositions in a close up situation.
Sharp focus is most important in case of a small flower. Macro photography is crucial and even a tiny movement for your shot can spoil the picture, as the depth of field is small. It needs to be understood that in macro photography, depth of field is a matter of millimeters. Therefore, much attention to focusing is something to be practiced and worked upon.
There should be no distractions in the background and foreground. Therefore, using a black sheet as a background can be useful. It is better to go for a tighter framing of the flower, either by using zoom or moving physically closer to minimize the distraction. Also, consider different angles and using different aperture settings to blur certain areas, as per your choice.