The key to make this look good is reflections. The tube of the TV give alot of great reflections that you will need on top of you footage in order to get what you are looking for. I start off by matching the colors and contrast. Then you will need some noise or scan lines something to dirty up the footage a bit. Then mask out the tube from the shot and lay it over the footage you are trying to insert and use a combinations of transfer modes and level adjustments to lay the reflections over the top. To top it off you will need some fall off in the corners so make sure your footage fades out towards the edges of the tube.
This is all about perception. If you can look at a TV and figure out what makes it look the way it does then the hard part is over with.
good luck
Vinnie