For day-to-day care, dish soap and water will remove debris from food or smudges from dirty hands, and a soft cloth-like microfiber or a paper towel will buff it to a shine. Acidic kitchen substances, like lemons or tomatoes, or bathroom staples, like toothpaste, can increase the rate of the tarnishing process. In these instances, you'll need brass polish (there are several commercial polishes to choose from) rub some onto a soft cloth, wipe in an upwards motion, rinse with water, and dry to keep your faucet looking its best. Brass is going to change eventually, no matter what you do, but you can keep it looking like the day you bought it longer by polishing it frequently.
There's one important detail to note if you turn to brass polish: Most formulas are corrosive to some countertop surfaces, like marble or wood, so be careful not to overdo it, especially around the escutcheons that join the faucet to the countertop. As a rule, we don’t recommend DIY mixtures, which can be abrasive and scratch the finish.
Depending on how much of a patina you want, unlacquered brass kitchen faucets can be polished twice a year or as often as once a month. If you find your unlacquered brass faucet tarnishes more quickly than you'd like, you can also consider coating it with carnauba car wax, which will seal the surfaces (and reapply as it wears off). With proper care, unlacquered brass should last a lifetime or longer.