Now is the fun part — cutting your tofu. How you slice depends on how you plan on preparing it. Diced works well when marinating, since the smaller bites result in more flavor per bite, but they can also be used when sautéing or baking. And since you've chosen a firm tofu, it'll hold its cube shape well.
Lucky for you, some brands offer precubed tofu, so that's one less step. All you'll need to do is slit the top of the package with a sharp knife to drain the water, and then you can use your hands to gently squeeze the container to remove the excess moisture.