If you've ever seen lighting in a pro studio, you'll have noticed that thelight sources are large, with either the flash being bounced from an umbrella or inside alarge softbox. The reason for this is that the larger the light source, the softer yourshadows will be.
If you want soft shadows, you have to make your light source larger. There are several ways to do this.
First, if you have a flash with a tilt head, you can bounce your flash off the ceiling (if you are indoors!), so that a large area of the ceiling becomes the source of the lightfalling on the subject.
Second you can add a diffuser to your on-camera flash. There are several types such asthose made by Lumiquest and Sto-FenThe Shell and Gary Fong'sLightsphere. All of these devices work by increasing the size of area emitting light and/or diffusing some of the light so it can bounce off walls and ceilings. The bounced light partly fills in the shadows making them lighter. The larger light souce softens the edges of the shadows.
The illustration shows the effects of various diffusers on the shadows cast by a grid in front of a white wall: