Lacquer is a protective wood finish. Black lacquer is commonly used on pianos and other fine furnishings. Glossy lacquer shows fingerprints and dust very easily, but you will find that most lacquered furniture, glossy finished or satin finished, is simple to clean and to keep clean--especially if you avoid letting anyone place moist items (water glasses, for example) on these pieces and you dust it frequently. You won't need a lot of cleaning products and only minimal water.
Dust black lacquer with a soft cloth. Use microfiber dusting cloths, or any other soft cloth (old T-shirt material works fine, too).
Dampen a cloth in warm water. Wring out the excess water and wipe down the lacquer, going with the grain. Follow the damp cloth immediately with a dry cloth, also rubbing with the grain. For normal cleaning, this is all you should have to do.
Clean remaining smudges with a damp, soapy cloth. You won't need much soap--just a dime-size drop. Any mild soap will do, but an oil soap for wood may work best.
Remove white rings (caused by water glasses) by either waiting a few days (if the ring is new), wiping it with a cloth dampened in mineral spirits, or using a lightly abrasive paste of mineral oil and baking soda, as suggested by coreycare.com.
Polish black lacquer only if necessary, and only if it is high-gloss, rather than a satin (low-gloss) finish. When you do polish, use a lacquer-safe polish (look for these at piano supply shops or home improvement stores). Spray the polish lightly on the cloth and wipe gently with the grain. You should avoid polishes containing silicone.