All you need is steel wool, some vegetable shortening, and about 10 minutes. First dip out about 1/4 cup of shortening onto a napkin or paper plate so you are not dipping into your cooking ingredients with a dirty hand. Then take about a teaspoon at a time on a section of steel wool and rub it into the exterior surface of the stove. If there are rusty patches, scrub them out with the steel wool. Cover the entire surface a section at a time, using fresh wool as it wears thin. Finish up by rubbing the excess off with paper towels or rags. It is amazing home shiny and new the stove looks.
Note: Oil is flammable, so use it sparingly and always rub off the excess. The first fire after conditioning your stove may smell a bit like your cooking, but that soon dissipates, particularly if you rub down your stove well after applying the oil. This method works well on the black cast iron models, but would not be appropriate for the enameled models. I do this at least annually, and sometime more if I am having guests and want to freshen up the stove's appearance.