Or you can shoot through gauze - coloured or nude. I've tried it and it works fairly well although you can get the effect just in photoshop.
If you are shooting outside, try to get a single flower on its own, use the largest aperture you can (smallest f-number) to get shallow depth of field, and a tripod (then you don't have to worry about shutter speed if the light is not so good). Don't shoot on a sunny day as you get horrible reflections on the petals - a bright cloudy day is best. If you are shooting in your own garden, then you can stake the flower out of shot if necessary and/or bend other flowers out of the way. And don't shoot on a windy day!