By Aaron Crowe, dealnews writer For something that has an average lifespan of 17 years and takes up a large chunk of a living room — and that you stare at a few hours each day — it’s surprising that many TV-buying decisions are made at the spur of the moment after just a little bit of browsing. There’s more to buying a TV — or at least a good TV — than buying a sweater or a pair of jeans. But that's exactly how shoppers are treating the decision. They see markdowns on prices and they simply pick one they want to take home after a little deliberation. This goes for buying online and buying in stores. The only difference is that they may, more often than not, ask for some help when they are in stores — just not much help. TV shoppers typically give a salesman just 20 minutes to make a pitch, according to Robert Cole, owner of World Wide Stereo, which has sold TVs since 1979. He says what’s really needed is an hour. If you're determined to cut it short, you need to arm yourself with these simple strategies so you can make the most of your short shopping time, and this especially goes for buying a TV online, sight-unseen. If you really want to make an informed decision, you're going to have to do a little in-person window shopping, even if you end up standing on the showroom floor of a store, and ordering one on sale after getting an alert on a price drop from the dealnews iphone app. Throw Out the Viewing Ratio Theory: “It’s really difficult for a TV to be too big,” Cole says. But that said, you don't really want a TV in your living room that's going to overpower everything else, and that will make you want to cover it with expensive furniture. There used to be a formula that said to measure 1.5 times the height of the TV set to see how many feet back you want your couch to be for the “sweet spot” of viewing. But now with HDTVs, Cole says, that idea is out the window and people should buy the biggest TV they can without it looking ugly. Do Your Homework: To figure out what will look nice on your wall, Cole recommends cutting out a piece of cardboard as big as the TV you want, and hang it up to get an idea of how the TV will look. If you're stuck in the old mindset that you need smaller TVs in rooms other than the living room, think again. Coles says that the days of the 22-inch bedroom TV are long gone and not most people are opting for 50" sets for secondary rooms. Tune Out: With so many televisions next to each other in a typical showroom, it’s difficult to envision what it will look like at home. “Turn the picture off and look at the machine itself,” Coles suggests. “And think, Is this what I want hanging on my wall?” Bring on the Decor: Shoppers should also keep in mind aesthetics that are unique to some manufacturers. For example, Samsung is known for slimmer televisions that are designer friendly, while Panasonic has thicker TVs than most, but better pictures displays. Pick Your Showroom Carefully: You want to go to a store where you can see how a TV looks in a living room setting, and not just in a row of other TVs on a wall. Consider the Ceiling: You want to pick a store that doesn't have glaring, awful lights. Since most people don’t have fluorescent lights at home, shopping for a TV in a store that has them won’t give you a fair idea of what you’ll see at home. Different wall colors also affect the in-store view, as does having many TVs reflecting off the screen you’re looking at. Gets Hands-On: Many stores set their TVs on “dynamic mode” with the color settings on high, creating a bright picture that will be overpowering at home, Cole says. Best Buy has one stream of video for all of its TVs, which may look better on some but not others. “You should see the TV in the real world somehow,” he cautions. So don't be afraid to take control of the remote and play with the settings. Get Your Game On: Another thing to keep in mind is what you’ll be watching on the TV: Sports and movies look great on an HDTV, but not all discs are created equal. You should check out how regular DVDs look as well as Blu-rays. Watching concerts will require a good sound system. If you have kids, you should also consider what Internet-enabled features come with the TV and how to exert parental controls on them. Think About It: By the time you’re ready to actually plunk down several hundred dollars, you should know a lot more about what you want from a new TV than simply how it looks in the store. You're making an investment that should last 15 years or more and will likely be a centerpiece of your living space, not hidden in a dusty basement. How long do you typically spend shopping for a new TV?Market Research Aaron Crowe is a freelance journalist in the San Francisco Bay Area. He has worked as a reporter and an editor for newspapers and websites. Follow him on Twitter — @AaronCrowe. Photo Credit: Zappowbang via Flickr.