Choose your fabric wisely since people may want to put up their feet (and shoes). Outdoor fabrics can be smart; steer clear of linen and fabrics with high amounts of rayon or viscose. Take a swatch home and test it out with dirt red wine or whatever you think your coffee table will encounter to make sure your fabric choice can handle it all. Keep an upholstered ottoman 18 inches from a sofa or chair so you can easily put up your feet and make sure the height is consistent with the surrounding seats.
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).