More distance between the background and the subject, and "barn doors" which are -- to me -- any fool thing that blocks light from going from the lights to the background while allowing unimpeded light to the subject. You can use big chunks of cardboard, blankets, whatever.
You can also snoot the lights, which has essentially the same effect but will affect the amount of diffusion you've got going on of course.
Definitely. Introduce light and shadow by putting the lights to the side, use a ratio to help with that, and that will provide more depth and dimension to the objects lit.
This will sound snarky, but: Just don't light it. Darken the room for the shoot, and control any light spill from the flash(es) with gobos, panels, anything you can find and use to block it from reaching the background.