Heat a heavy rectangular griddle or (2 skillets) to two different temperatures: 1 side (or 1 skillet) over medium to medium-low, the other over medium-high. Line a tortilla press with 2 squares of plastic that just cover the plates (the thicker plastic from food storage bags is easier for beginners to work with).
Knead the masa (either fresh or reconstituted) with just enough water to make it soft (like soft cookie dough), but not sticky. The softer the dough, the more moist and tender the tortillas—but don’t make it so soft that more than a bit sticks to your hands.
Open the press and lay 1 square of plastic on the bottom plate. Scoop out a walnut-size piece of dough, roll it into a ball, and center it in the middle of the plastic. Cover with the second sheet of plastic. Close the press and use the handle to flatten the ball into a 5- to 6-inch disk. Turn the plastic-covered disk of masa 180º and press gently to even the thickness.
Open the press and peel off the top piece of plastic. Flip the uncovered side of the tortilla onto your palm, lining up the top of the tortilla with the top of your index finger. Starting at the top, peel off the remaining sheet of plastic. A portion of the tortilla will be dangling off the bottom of your hand. Quickly, lay the tortilla onto the cooler side of the griddle (or the cooler skillet): don’t flip it off your hand (that always results in rumpled tortillas); instead, as you slowly sweep the tortilla away from you, let the dangling part catch on the hot surface, then roll your hand out from under the tortilla (the movement looks a little like your sweeping something off the griddle with the back of your hand).
Bake for 15 to 30 seconds—just until the tortilla releases itself from the griddle. It’ll look just a tiny bit dry around the edge, but don’t leave it too long or it will turn out dry and heavy. Flip onto the hotter side of the griddle (or hotter skillet) and bake until splotchy brown underneath, 30 to 45 seconds. Turn once again, still leaving it on the hot side, and bake another 30 to 45 seconds to brown. During these last few seconds of baking, a perfectly made tortilla will puff up like pita bread. If yours doesn’t, it may have been baked too long on the first side, may not have been pressed evenly (or be too thin or too thick), or may not be on a hot enough surface. Though an unpuffed tortilla won’t be as light, it will still be good.
Transfer to a cloth-lined basket and continue making tortillas, stacking them one on top of another and keeping them covered. As the cloth traps the steam, the tortillas will complete their final little bit of “cooking.”