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).
If you get a tufted ottoman consider the depth of the tufts — especially if you expect to eat on it. Crumbs will find their way into the tufting and are not always easy to get out. Round coffee tables aid circulation especially where there are many available seats as in this example. If not every seat can reach the table make sure there’s another surface at hand.