Carpet the floor and add more furniture.

I'm guessing that your space is basically rectangular. For sound reflection that is the worst shape. Anything you place to break the reflections will help. Curtains on windows, pictures on the walls and as the previous poster suggested furniture or carpet/rugs.

We took advantage of these things and even have some angular furniture arrangements and have no distracting sound reflections. Photos linked from "My Page" may provide some help.