While teaching up in Maine this past September, I demonstrated a proper bounce technique for a few of the students. We came downstairs from the studio to the new Maine Media Gallery on the main floor of the Shepherd Building in Rockport.
I think of a bounce as a flat screen softbox, place your bounce where you might have placed a softbox had it been on a stand. When you bounce, it is imperative that you prevent any RAW light from your flash from reaching your subject. The only light that should be lighting your subject should come from the bounce surface itself.
In the photo above, on the right side you can see the strobe. I have placed a flag or gobo on the side of the flash closest to the subject. The strobe is lighting the adjacent wall on the left of the frame. The wall which is lit, now becomes my flat screen softbox.
Here is how the subject looked before using the bounce. In the final image shown at the top of this post, the fill on the subjects face was provide by the light bouncing off another white wall on the subjects left side.