Rules for choosing the right size rug for your rooms

Runners
This protects wood floors while adding warmth and softness to high-traffic areas like stairs and hallways.  The standard size is 2' 3" x 8'. To get the placement right, allow at least 4" of space along the sides of the runner parallel to the walls or edge of steps.
In a corridor, keep a close eye on proportion. Standard runners may be too narrow, so fit accordingly
Just remember that the gap between rug and walls should be no more than one-third the width of the runner.

Accent rugs are small (usually 2ft x 3ft), adding instant color and pattern and they can be moved whenever you feel like it! To position an accent rug the right distance from a piece of furniture, wall or cabinet, take the width of the rug and divide it in half. The number you're left with is the maximum distance the rug should be placed from the furniture. Think about using two or three rugs in complimentary colors to break up a long, narrow hallway or corridor.

The next best thing to a wall-to-wall rug is a full-size one. If you want to showcase the floors, pick a rug that is smaller than your room. As a standard decorator rule a full-size rug should be placed within 18 inches of at least two of the walls, if you have cabinets or book shelves then measure for the edge of those instead of the wall. The legs of the main furniture pieces should be on the rug. Make an exception for wall-hugging pieces like a large china cabinet; this should be completely off the wall. Picking a full-sized rug in a centralised position in a room helps bring attention to its main focal point.