Generally, it's not the
playing of a piano that causes it to go out of tune.
Changes in the environments temperature and
humidity, causes the wood of the soundboard to expand and contract, which in turn throws your piano
out of tune.
To keep your instrument and investment in top shape,
I recommend to get your piano looked at at least every two years.
Regulation involves alignment and adjustment of all
mechanisms inside your piano.
In some cases, you might also want to get your piano
re-voiced to adjust the overall tone and sound of your instrument
to your preference.