A good homemade brass cleaner is a mixture of salt, vinegar and flour. Mix 1 teaspoon salt into 1/2 cup vinegar, then mix in enough flour to make a paste. Rub the paste on the brass, and let it sit for 10 minutes. Rinse the paste off and buff dry.
Another option for cleaning brass is to rub ketchup over the tarnished spot with a soft cloth. Then, rinse the ketchup off the brass. A paste made of equal parts salt and cornstarch, along with lemon juice, is also an option. For a tarnish that is tough to remove, baking soda rubbed on the spot is an alternative.