Place your sectional sofa opposite to the main area in the small room. This directs everyone's gaze toward the focal point in the room. This may be the TV, a piano, an attractive view, a fireplace or an architectural feature.
Arrange all other pieces of furniture after placing the sectional in the perfect spot. This prevents you from having to move the heavy sectional multiple times before deciding on a position.
Position the sectional so that any L-shaped features don't block a doorway or a walkway through the room. Doors may not open fully, and someone walking through a conversation area is distracting.
Remove end tables from the room if the sectional has a section you can flip down to provide a place to set your drinking glass or other accessories. This provides more space in the area.
Separate pieces of the sectional -- if yours has this option -- and utilize the other sections in the small room to form a U-shape around the focal point. This creates an intimate and cozy conversation area.