I think the biggest mistake people make when venturing into the world of tofu is buying the wrong texture. If you want a dairy substitute for smoothies or cold dips, go with silken. If dinner is what you are looking for, choose extra firm. Knowing how to cook it is the next hurdle.
For extra firm tofu, cut it into slices. I usually cut 6 slices if I am putting it into stirfry (cut it into cubes after it is cooked); 4 if we are eating it on its own. Take a clean dish towel folded in half, place slices on half and fold the towel over the slices. I like to place a cutting board on top for some added pressure. Getting some of the water out will help it crisp up and give it a better texture. Let it sit for at least 10 minutes and flip the whole towel package over half way through; the longer it sits the better.
In a large non stick skillet or griddle over medium heat 2 tsp-1 Tbsp of oil. Place tofu in it and let it cook for a 3-4 minutes. Flip it and use a large spatula to firmly press the slices down. This helps more of the water cook out and ensures a crispy texture. Flip and press several times during cooking. Seriously, don't be afraid to press down hard and hold the turner there for a little. you as much water as possible to cook out. When both sides are crispy it is done! For 6 slices, it usually takes about 15 minutes to get the perfect texture.