The Rebel:
People with good powers of perception don't focus one one aspect of their observations. They don't take things at face value and base their conclusions on a vast array of information and try to form conclusions based purely on what they consider to be facts. A well trained soldier for example is taught to quickly observe his surroundings, evalute them and how his current situation relates to them, try to decide firstly what he does know for certain and then calculate all the plausible possibilities. Once he feels he has made an accurate evaluation as possible, he will plan his next move. It is not possible to be a great tactician without being skilled at perception. Fortunately people are able to be trained to be better at perception but it demands a lot of self-discipline.
Luminosity has a great app for training your brain, and getting yourself into good habits like forcing yourself to learn and ask questions, playing games of observation while just walking down the street or sitting in a restaurant, drawing conclusions then comparing them with the conclusions of others and learning how they arrived at theirs all teach you how to be perceptive.
So next time when the TV is on consider immersing yourself in a game of perception because it is a skill and a life tool you have to keep practicing. I know I need a lot of practice.