What should be done to maintain an upright piano?
I am not asking about tuning it, but what can be done so it does not have to be tuned as often?
I heard someone once say about a particular piano that the strings should be oiled.
Are there things that can be done to help prevent the keys from sticking?
If so, how should it be done, and how often?
All pianos benefit from being in very stable environments, not too dry, not humid, and a static temperature. This will help to keep it in tune for longer. Realize though that playing the instrument will knock it out of tune and the more you play the faster it will happen. Also, if the pin block is shot, it will go out of tune fast no matter what you do, because the tuning pins will slip. Additionally, regular tunings will help keep it in tune longer. I know that sounds a bit silly but it's true. If you wait until the piano is REALLY out of tune, the tuner will have to move the pitch farther which will stretch the strings and make them less stable.
In short the best thing to do is control the environment, and get it tuned regularly, twice a year is enough for most pianos. There isn't really anything else you can do to keep it in tune longer.
Also, do NOT oil the strings. This is the quickest route to spending tons of money to replace the strings.
You can get a climate-control system installed in the piano. Dampp-Chaser is one brand. It has both a water system to increase humidity and a header to decrease humidity, and works automatically to increase or decrease as necessary. In addition to helping the instrument stay in tune, it will help prevent sticking keys. The cost is several hundred dollars, so it's worthwhile only for a very good piano.
In addition to ecline6's answer: In very dry places (large appartment houses typically), you can place couple glasses of water into the piano to keep the humidity at a bit higher level. You obviously have to add water to the glasses from time to time, it usually lasts about a month.
There are 3 reasons:
Wood in general doesn't like too dry places.
During the summer, the humidity often rises rapidly for short periods of time, and you reduce the shock to the piano by keeping the water inside.
The water itself (and the wet air) slightly stabilizes the temperature inside the piano, helping to reduce the temperature shocks it might get. Remember that slow change from 18C to 25C is much nicer to the piano than a fast one.
