We just got our floors sanded and refinished with polyurethane and I got a little on my shoe and tracked some footprints on the dry floor, how can I get these off?

So you tracked onto the finished area?

If so, then best bet will be to do some light sanding and then brush on some polyurethane over where you did the sanding.

Use 400-600 grit sandpaper for the sanding... and don't go beyond just dulling it up to remove the footprint... and then use a paintbrush to touch it up with fresh polyurethane.