One of the most common questions I get is:  How often should my piano be tuned?  The answer to that question depends on your particular situation.  A piano in a performance situation should be tuned before every performance.  Most manufacturers recommend that the piano be tuned every six months.  A new piano should be tuned three to four times in the first year to let the strings settle in and give the piano a chance to stabilize.   The environment a piano is in has a lot to do with the stability of the piano.  A comfortable temperature with stable humidity will help the piano stay in tune.  

Matt Shoemaker
Piano Tuning and Repair