No-Cost Lighting Tricks to Improve Your Digital Photos
Tape a clear 35mm film canister over the flash head (see this figure).
This works best if you have only a small, fixed flash. You can also place a sheet of facial tissue inside the 35mm film canister that you attach to your flash, diffusing (softening) the light a bit. Or you can also use colored tissue papers to change the color of the light the flash produces.