Children are particularly susceptible to advertising, so the FCC has ruled against "host selling." This prohibits TV characters from endorsing a product in such a manner that prevents children from distinguishing between the program and the ad.
TV was once filled with ads for cigarettes and other tobacco products. If you watch reruns of "I Love Lucy," for example, you'll see Lucy and Ricky frequently using cigarettes provided by their sponsor. This ended in January of 1971, when Congress banned TV ads for cigarettes.
The government is not the only body creating rules regarding TV ads. The NCAA, the body that oversees college athletics, has set limits with respect to how much beer advertising is permitted during broadcasts of college sports games. According to the Broadcast Law Blog, the NCAA requests that beer ads should represent less than 60 seconds of commercial time per hour. Further, the NCAA doesn't want hard liquor advertising to be shown during their games.
As summer turns to fall, you start to see countless political ads made by people hoping to influence your vote. In order to keep things fair, the FCC has established some rules. TV stations cannot charge candidates more than they charge other advertisers, for example. Stations must also allow all candidates equal time. For instance, if a station interviews a candidate for a news report, they must also provide the same opportunity to other candidates.
During your favorite shows, you may have noticed a character, say, walking through a supermarket and stopping in front of a giant, well-organized display of a certain product. It's likely that the company has paid the producers of the TV program to feature their product in the show. The FCC, according to USA Today, is considering new rules to ensure that the viewer is aware if a company has paid to get their advertising message across. These ads are particularly popular because you can't zip past them on your DVR because they're actually in the show.