Although it seems that deciding where to put a television is a bit of a no-brainer, there are actually quite a few things to take into account in order to give you a comfortable and healthy viewing experience.
The TV must fit in with the aesthetics of the room: it must not clash with any other furnishings, or be untidy, or make the room seem out of balance. It should compliment the furnishings of the room if possible.
You need to get power to the TV, so if possible it should go near an electrical outlet point, or else (to keep the room neat) one would have to put in some power skirting, or "trunking" to house an extension wire to a where the TV is going to be.
You need to get picture to the TV, either from an antenna or dish, or from cable. If you are using an antenna, it is best to keep this cable as short as possible to minimise losses in the cable. If you have a very strong incoming signal, then this issue is not so important. If the signal is bad and the cable has to be long, get some low loss cable to compensate. Note, however, that low loss cable is quite expensive.
Glare on the screen from windows, lights and reflections is a very important issue, as glare reflecting off the screen into the viewers eyes is not only irritating, it's also bad for you, causing eye strain, headaches and vision problems. Make sure that the TV screen does not face any windows or bright lights, or pick up strong reflected light from surfaces like glass or metal. Sometimes just tilting or angling the screen slightly can eliminate a lot of glare.
Try and get the TV screen at the same height as your eyes will be when you are viewing it, at which time you would normally be in a seated position, as this will be the most comfortable height for viewers.
Make sure that the TV has enough ventilation, by leaving enough space around it. The TV installation manual will give you the exact space to leave, but normally 5 to 10cm or 2 to 4 inches on each side, and at the back, should do it. If it's a flat wall mount screen, space at the back is not necessary, but leave some air space at the top of the screen, and at the bottom if there are air intake vents there.
So as you can see, there are quite a lot of things to consider, but they do help to give you a better viewing experience, and lengthen the life of the TV set.