As well as being a musical instrument, your piano is a beautiful piece of furniture. Keeping it looking its best is one of the most misunderstood parts of piano care. Let me assure you that while there is no single answer to that question, it doesn't have to be that difficult either.
Pianos come in several main finish types. The most common one today is high gloss polyester. As little as 20 years ago, in many North American markets, selling high gloss pianos was very difficult. Nobody wanted them. Today, the pendulum has swung completely the other way. Many piano stores I have been in lately don't have anything else on the floor. The "old school" satin lacquer finish is nowhere near dead, but it certainly is losing the battle in terms of sales numbers.
What finish to buy is entirely a matter of taste. The finish has no effect on performance. If you like shiny, buy shiny. If you don't like shiny, buy satin. Each has their own strengths and weaknesses when it comes to piano maintenance or repair.
Find out for certain which type of finish your piano has before doing anything to the finish.
Let's start with the high gloss finishes. If your new piano is very shiny, it is almost certainly finished in a thick coat of highly polished polyester. You can find high gloss lacquer finishes, but they are in the minority. Know for sure before you attempt to clean or polish your piano. I will address the polyester type of high gloss finish. Polyester finishes are very hard and thick. They are extremely durable in most ways. A small spill will have no detrimental effect on the finish. Please don't experiment with this at home to see if I'm correct; you don't want liquids near the piano. Trust me that they are water impervious and nonporous. You still do not want liquids getting into the piano. Since so many modern pianos are black (called ebony polish in piano sales speak), they tend to really show dust. I suggest using a very soft dusting tool such as the California Car Duster, which can be purchased at any auto parts store. If you follow the directions for getting it ready for use, it will last almost forever and become your favorite duster for the whole house. Once the piano is dusted, use a polish that is specifically for high gloss piano finishes. There are several good ones out there. DO NOT use common household furniture polishes. EVER!!! Spray the polish onto a high quality microfiber cloth and wipe down the piano. These polishes are almost miraculous in how they deal with finger prints and smudges and will not streak. Most manufacturers have specific finish care instructions on their websites as well. Never spray the polish directly onto the piano itself, or even in the direction of the piano. If the polish were to land on or near the tuning pins or various other parts, you could have a big problem on your hands. Once you've got the hang of it, even a large grand piano can be spiffed up in a couple of minutes.
Many domestically made new pianos and the majority of older pianos have a much less glossy or satin finish. This type of finish is usually made of lacquer. It is different than the polyester type in that it is very porous and will absorb water or any liquid that may land on it. Wipe spills immediately or the liquid will penetrate the finish and may cause the glue holding the veneer to let go. This can produce unsightly bubbles in the finish. Do not use the same type of polish on a lacquer finish as you would on a polyester. There are many different types of lacquer out there and each has slightly different maintenance requirements. If the finish has not been polluted with furniture polish, it's usually best to dust with the duster mentioned above and wipe any smudges with a very lightly dampened soft cloth. Rub along the lines of any grain, never across. Wipe with a dry cloth immediately after.
Please resist the temptation to clean inside your piano. There are many delicate components inside that can be easily bumped and knocked out of place causing the piano to not play properly. Many common household cleaning chemicals and liquids will do great harm to your instrument should they be applied to the wrong place. Leave the inside to your technician. Ask them to clean the inside when they come for the next regular service.
Other finish types do exist, but these two cover the vast majority of pianos out there today. Please consult your technician or the dealer you purchased the piano from to determine the best cleaning methods for your specific instrument.
Or, if all of that advice doesn't appeal to you at all, grab your brushes and paint and have some fun!