Here is a before photo of a living room and its television.
An obvious solution is to avoid photographing the television. However, if that's not an option, adding an image to the television can add a nice touch. How about inserting a photo from the exterior of the house or adding a lovely landscape from a local park?
Keep in mind that if you choose to replace the blank television screen, use an image that you own the copyright to. Also, let some of those screen highlights show through so the final result is much more realistic.