Use the tables, put on table cloths and candles. Turn off TV's, Video Games, cover the pool tables, etc. Make sure you have a stage. Even small rooms need a stage, but make sure it fits in scale with the room. Make sure you have stage lights.
Lights help the audience focus on the performance.
Know how to turn off the room lights. Make sure you understand the sound requirements and have taken care of them if you are providing the sound system. If the act is doing their own sound, schedule a load-in and arrange for a few strong backs to help carry in equipment. Allow them time to do their sound check, and get it right. Then make sure you have some help to load-out after the show.