If your tomatoes are not exceptional, you can toss them in a little salt and drain them in a colander for 15 to 20 minutes before using.
Italian cookbook author Marcella Hazan also adds anchovies and capers to Panzanella. Although not traditional, they are worthwhile additions and I sometimes sneak them in, too. If you want to add them, use 1 tablespoon of capers, rinsed, drained and minced, and 3 to 4 anchovy filets, minced, to the dressing in step #3.
Note: Panzanella can be served soon after it's made but it's also fine to keep it at room temperature for several hours, making it a perfect do-ahead dish.