Your piano should be placed in a position where influences such as dampness, proximity to fire places, underfloor heating,direct sun light or constant drafts is minimised. These are factors which are most likely to affect the long term function and appearance of the instrument.
Other considerations are Surface Environment and Accessibilty.
Surface Environment: The piano is an acoustic instrument and for maximum tonal response it should be in a position which is not essentially composed of hard surfaces.
Accessibility: If the piano is required for general family entertainment / recreational use it needs to be placed where this can be achieved. If however it is for tuition purposes of a single member of the family , it can be placed in a bed room or a room which provides both privacy for the student and does not disturb the rest of the family.