Set your DJ system up for optimal sound by setting up your coffin facing the room along a wall but not all the way in the corner.
Place your primary speakers on each side of your decks, leaving 2 or 3 feet of space to each side, enough room to wiggle through. Set up your subwoofer for the best sound by giving it enough room to stand free without piling any gear on top of it.
Set the levels in your headphones until everything sounds nice and even, then remove your headphones and try to set the room sound from your vantage point to achieve the same sound. Getting this right involves knowing the limitations of your equipment, but you'll have time to reset the levels later so don't sweat it too much.
Walk through every inch of the room where you are trying to set your DJ levels, with special emphasis on dining and dancing areas. Are there dead spots, or areas where the sound coming from your DJ booth sounds muddy and dark?
Angle your primary speakers ever so slightly to hit these spots. You won't have a perfect sound everywhere in the room; the key here is to make sure your DJ equipment is aligned to sound correct in the most important places, which are the dining area and dance floor.
Ask a friend to walk through the room now that you have your coarse DJ equipment alignment done, and crank your system up to full volume. This "sound check" is designed to create the noise conditions you will experience later on at the gig.
Converse with your friend to see how the DJ equipment sounds from each area once again. Make adjustments to the volume and levels as necessary.
Be flexible throughout the night. If the hosts ask you to readjust the levels or spacing of the DJ equipment, remember that you are there to provide a service and give the people what they want.