Make several small incisions in potatoes with a knife. Rub oil or butter lightly all over each potato, then roll each potato in a little salt. Place potatoes directly on the oven rack, and bake at 375 degrees for 45 minutes for medium to large potatoes. Turn the potatoes over halfway through the baking time to ensure even crispness and avoid darkening on one side. Remove from the oven when baking time ends and cut or squish the top of the potato open.