Drain tofu and cut into cubes or desired shapes. Press for at least 30 minutes with a clean, lint-free kitchen towel or a few paper towels. (I recommend against skipping this step! The oil will splatter much more if there is a lot of excess liquid in your tofu, which can be dangerous. It can also take longer to crisp up.)
In a mixing bowl, whisk together cornstarch, salt and pepper, and optional spices. Add in the pressed tofu and toss to thoroughly coat. (As a shortcut, I like to place all the ingredients in a container with a lid and shake it until the tofu is fully coated.) Let the tofu sit in the cornstarch mixture while you heat your vegetable oil.
In a heavy-bottomed skillet or cast iron pan, heat at least 1/2" oil to 350°F. (I highly recommend using a thermometer to ensure the oil is hot enough! If it's not, your tofu will take longer to fry and may not get as crispy. It will also retain more oil.) While the oil heats, prepare a tray with a wire cooling rack (my preference) or a paper towel-lined plate to let excess oil drip off.
Carefully add tofu to the oil and fry 3-5 minutes before flipping and frying for an additional 3-5 minutes. The cornstarch coating will be crispy and light golden brown when ready.
Remove to wire cooling rack or paper towel-lined plate. Toss with sauce of choice and serve while still hot and crispy.