So the piano movers have just arrived with your new pride and joy. Congratulations! "Where do you want us to put it?" they ask. "Right over there by the window", is your reply.
Let's think about this for a minute. Where a piano is placed in a room can have a tremendous effect on its ability to hold tune and its longevity, and thereby your enjoyment of the instrument.
Never put a piano where direct sunlight can come in contact with it. UV light and the heat cycles created by the moving sun will be very damaging to the finish and will greatly decrease tuning stability.
Never put a piano in a location where a ventilation register can blow hot or cold air directly on it. The dry air coming from your furnace or AC can be harmful to something made mostly out of wood.
It is becoming a bit of an old wives' tale that placing your piano on an outside wall is a no-no. Today's modern homes tend to be quite well insulated, so this is usually not a problem. A simple way to check is to place your hand on the wall. If, on a cold day, the wall feels significantly cold to the touch, don't put your piano there. If it doesn't, go ahead. Remember to leave the piano 3 inches or so from the wall.
Placement near an outside door is also a poor idea. The sudden and severe temperature changes that rush in when the door is open and no piano humidity control will have negative effects too.
If you avoid these few simple pitfalls, your piano will thank you by giving you countless hours of enjoyment.
BTW, this is an example of relatively poor piano placement.