It's a fact of life: Brass is going to tarnish, as sure as the sun is sure to shine. To address tarnished brass, you don't need to employ a toxic polish. Simply wipe your brass item with a little lemon juice, and it’ll shine like a freshly minted penny. If your item is brass-plated, not solid brass, don't try this method—stick with soap and water or you could damage the plating.
Related: How To: Restore Brass Hardware