Don't go "cold turkey." If you're accustomed to watching four and a half hours of prime-time TV each night, unplugging your set and stuffing it in the closet is a sure recipe for acute withdrawal. If your aim is to completely erase TV from your life, start slow. Turn on the set a half hour later each evening and turn it off a half hour earlier than normal.
Find a hobby. Four-plus hours a day is a lot of time to fill, so you should have something fun and engaging to fill it with. "Read a book" is the usual cliché, but very few people have the attention span to read a single book for an entire evening. Try listening to music, painting your bathroom, playing with Legos--in short, anything to get you off the couch.
Try "appointment TV." Too many people "sort of" watch TV-you know, flipping idly through 500 cable channels, desperately hoping to find something interesting to watch. Instead of playing this fruitless game, resolve to watch only those shows you know you want to watch-like "The Sopranos" or "CSI." Turn the TV on promptly when the show starts, and when the show's over, turn the TV off.
However, don't make too many "appointments." An amazing number of TV shows demand constant, beginning-to-end vigilance, such as "24," "Rome," "Lost," etc. Unless you want to keep spending half your life in front of the tube, choose only one or two "appointment" shows and forgo the rest. At worst, you can catch up with them later, when the complete seasons are issued on DVD. And speaking of DVDs...
Use your DVD player. Although many experts would say watching DVDs is only marginally better than watching broadcast or cable TV, at least DVDs have a clear beginning and end, as compared to the 24/7 TV smorgasbord. If you must, watch one movie every night. If you start getting up to two or three, though, you've simply replaced your six-hour-a-day TV habit with a six-hour-a-day DVD habit.