Once your new piano is in your home, find a place for it where its mechanism won't be exposed to abrupt changes in temperature. Don't put it next to a frequently opened outside door or in front of a picture window, and don't put it near heating ducts or radiators.
A temperature of 72 degrees Fahrenheit and a 40 percent humidity is ideal for a piano. Talk to a technician about controlling these factors.
Tuning
After you move a piano from store to house, or to any new environment, wait a few weeks for it to become acclimated before having it tuned. The first year, tune it four times, with the change of seasons, and have it tuned at least twice a year after that. A piano's continued good performance depends on regular maintenance.
Dusting
Ask your dealer for a book of care instructions for your piano. Dust the outside of the piano about once a week with a soft cloth, following the grain of the wood, and clean the keys with a sponge dampened with water or a very mild soap.
Inside
Don't tinker with the inside of the piano; don't use bug sprays or mothballs inside, and don't try to oil it yourself. Also, don't set drinks or flowers on top of the piano. If liquids spill inside, they can cause metal parts to rust and wood parts to stick. Have the inside cleaned professionally once every three years.
One of the best things you can do for your piano is play it often. Frequent use will prevent dust from accumulating, and retard rust. And anyway, isn't that why you bought it?
Additional Resources:
The Piano Book A wonderful source of information about buying a piano.
Del.icio.us