For a perfectly square table you may be tempted to use four matching pieces for a perfectly symmetrical look. However you can get a more intriguing look by using two pieces or groups one in each corner. Try a tall vase or lantern in one corner with a stack of two or three books in the other (and an airy sculptural accent on top).
When you have two sofas or any larger seating arrangement a big coffee table might seem like the obvious solution. But also consider a pair of matching coffee tables. They will keep the focus off one large piece of furniture and let your eye move around the room more easily. One classic coffee table size is 48 by 24 inches so you can plan on that when thinking about your furniture arrangement. A large coffee table is often double that: 48 inches square.