Modern pianos will hold good tuning for about a year.
Autumn and spring are the optimum times to have a piano tuned.
During the cold months a hot cup of tea goes down well with the job of tuning...

Ideally not too close to heating radiators or hot air ventilators.
Keep out of direct sunlight coming through a window as this can bleach the casework and split the soundboard. An internal wall is best.

If you have an older piano the keys may be Ivory, theses can discolour and go yellow if the fall (piano lid) is kept shut.
The modern covering of key tops is mainly plastic, these you can gently wipe over with a soft cloth using a little wax free spray sprayed directly onto the cloth.
Your tuner will be happy to clean keys for you while his/her cup of hot tea is cooling.

Grand pianos can get dusty inside, and on the soundboard. The job of cleaning should be done prior to tuning.
Your tuner will need to remove the piano action and vaccuum away loose dust and wash the soundboard.
I always find a chocolate muffin an ideal a complement whilst tackling this task
(home made cakes always welcome).

This probably means your tuning pins have come loose.
On older pianos this can be a result of central heating drying out the tuning block, causing it to swell and loosen the tight grip of the tuning pins. A simple solution can be to add Pin Tight to the tuning block, or alternatively by replacing all of the tuning pins with a larger size. For this, the piano needs to come into the workshop.