Cover each table with a disposable colored tablecloth. One idea is to use the school colors. If the school has two colors, alternate tablecloth colors on every other table.
Sprinkle graduation confetti on each table. Graduation confetti is large pieces of confetti that are shaped like graduation hats, diploma scrolls or the year that someone is graduating. Stick with your party's theme, and choose confetti that matches the decor.
Put a centerpiece on each table. You can purchase prefabricated centerpieces online, or from a party store, but you can also create your own. Stick flowers in simple vases, tie balloons to weights, or put candles in the middle of each table.
Set a photo album, consisting of pictures of the graduate, on each table. These will act as both decorative objects, as well as conversation pieces for the guests.
Place a few small bowls full of candy at each table. These will add a splash of color to the party, and help stave away guests' appetites until dinner is served.