The media tells us what to believe is important by only discussing what they think is important. I remember when Elizabeth Smart was kidnapped. At the same time, another girl went missing under suspicious circumstances, in my town. The media only discussed the Smart case and not this other girl. I found it very disturbing that one girl's safety was placed above another. I truly believe the Smart case was discussed more because she was a pretty girl from an upper middle class family while this other girl was from a lower income family with little support. I think her families resources fueled her media coverage.
The media defines "beauty" for a society. Look at the average body type of people in the movies, on TV and in commercials. They are mostly fit, thin and young.
There has obviously been a ton of buzz about the negative effects of the media's portrayal of "healthy" women in the past decade (maybe longer). Even though awareness has been brought to it though, you can see from the majority of the models on the covers of magazines in a check-out line that the image is largely remaining the same.
It is very subtle manipulation through the overshowing of a typical image.
There will be many answers to such a question. Be prepared to sift through them. I would say that one way in which the media manipulates messages and/ or constructs meaning through them is within the idea of gaining audience. While the media is committed to bringing the news to individuals, it highlights the stories that will increase or generate interest amongst the public. For example, there might be a conscious choice to steer clear of the issue of violence in cities and focus more on a "juicy" story involving a politician and a prostitute. The media covers both, but in spending more time on the latter, a subtle manipulation transpires and meaning is constructed. In the end, this is one way that the media manipulates messages.