There are a number of factors that will play into how often your piano should be tuned. Most manufacturers recommend twice a year, and that is a good rule of thumb. Humidity is the biggest enemy of tuning stability, and if you control the pianos environment well, the tuning may last longer. Tuning at least once a year is important to create stability for the instrument. Concert pianos are tuned multiple times for each concert! New pianos also require more frequent tunings, as the strings require time to stretch and settle.
What makes my piano go out of tune?
The single most important factor is humidity. During the summer, the increased humidty causes the soundboard to swell, sending the pitch of your piano sharp. In the winter the board dries out, and the pitch drops. The amount the piano is played will have some effect on the tuning as well. Heavy playing can also cause the tuning to drift.
My piano doesn't sound like what I hear in recordings, can that be fixed?
If your piano doesn't sound quite right, there are several factors: Tuning, Voicing, and design.
An out of tune piano may not sound quite right. The piano may be roughly in tune with itself, but if the pitch is quite off the piano may sound "wrong".
Pianos can be voiced to make them sound brighter or more mellow. Two pianos of the same make and model can be made to sound quite different from one another. If you are unhappy with the tone of your piano, it is possible that it can be changed to suit your tastes.
Some pianos simply won't sound as nice as others. A spinet piano has a distinctive sound, one that is much different than that of a concert grand. Some pianos are designed better than others, and there is very little that can be done to change it. During restoration, some design elements may be improved upon, but you may be limited by the original design of the instrument.
My piano is quote old, should I have it restored?
Restoration can be a very extensive process, and requires lots of consideration. While most pianos can be rebuilt, it might not be the best financial decision. A high quality piano with a very reputable name can be rebuilt, and the piano will be worth more than the money invested in the restoration. However, some pianos can be rebuilt quite expertly, but not worth the money invested if you were to sell the piano after. You must consider what sentimental attachment you may have to the instrument when considering restoration work.
You would likely be able to buy a new Asian import piano for less than the cost of an expert restoration, but the quality of a fine rebuild would likely be higher than a cheap import. The rebuilding process can take hundreds of hours, and the craftsmen involved take great pride in their work, accepting only their best efforts.
Should I get a free piano from Craigslist?
You may be able to acquire pianos for free or very little money, but keep in mind these pianos are priced this way for a reason. The piano may be able to be tuned, but they often require much additional work to get them into good playing condition. I would advise caution when acquiring any piano, and suggest that you have the piano looked at by a technician to assess its condition, and advise you on you much additional work the instrument may require.
Sometimes you can get lucky, but most free pianos I've encountered need quite a bit of work to get into good playing condition.