You want the kind of tofu they sell in the refrigerated section thats packed in water. Nasoya and Soyboy are both good brands. DO NOT buy Mori-nu aseptic pack tofu (even if someone stuck it in the fridge), because they are SILKEN tofus, and though they have an extra firm silken, it's an entirely different thing. (Mori-nu is good for things like dips, desserts, and smoothies, but don't hold up to stir fries etc..)
Once you get it home, drain the liquid off the tofu and press it. To press it, slice the tofu into whatever thickness it needs to be for the recipe (if it needs to be in cubes, then slice it, and cut it the rest of the way after you press it), and put it between two plates that nest, or two cookie sheets that nest with a few layers of paper towel or a kitchen towel under and over it. Then put something REALLY HEAVY on top. I use a cast iron grill pan. A full kettle works well, so do heavy books. Whatever you've got around that will weigh it down. Leave it for at least a half an hour, then proceed with your recipe.
How is the recipe using the tofu? I might be able to give you more tips if I knew how it was going to be used.