Soundproof the room. Insulate the walls, put up drywall and put soundproofing panels over the drywall. Your soundproofing job should be visually appealing and neatly done. If the job is sloppy (i.e. the drywall doesn't look professional or the panels look unfinished), it takes away from the organized and pleasing feel of the room. The control room needs to be soundproofed because you need the most accurate and true sound coming out of your speakers during the mixing process.
Put in wood floors. Wood floors provide a clean, neat and classy look to the control room. If you don't want real wood, wood-like material is cheap and easy to put in.
Put in uniform furniture. All couches, chairs, coffee tables, desks, etc. should have a uniform look -- whether they match or are all the same color. Your furniture should not be distracting, it should be an afterthought. Browns and blacks often are effective colors for control room furniture.
Create an ambient mood with the lighting. Never use florescent lighting as it can be too bright for a creative environment. Purchase lamps, artificial candles and other ambient lighting. Lighting adds more than people realize, and this aspect often is not given the attention it needs.
Put in a window to the tracking room so the engineer can see the musicians. This will help the engineer communicate with the musicians while seeing who is performing which parts.