Distance?Diffusion?Smaller effective light source?Larger effective light source?Lower ISO?Wider aperture?
As stated, the larger the light to the subject the softer the light.. Think about a cloudy day V a sunny day. The sun is the same each day and the clouds make up the diffuser. So, if you think about how to make a larger light it becomes a craft project. With digi cameras setting the iso to a larger number will help as the light will be less from the light source due to the need to light the larger diffusion. This is where the powerful studio flashes come into play.
Distance works, but I find that diffusion is the most effective.
Diffusion panels and screens. Two screens with a few feet between then works really well also.
