If you want to be a truly informed media consumer, always keep your eyes open for bias. It's everywhere, even when you think you don't see it.
And I'm not just talking about simple political bias, which is the most obvious and serious form of bias in our media. I'm also referring to:
Intellectual bias -- "experts" tend to reject ideas or solutions from outside their discipline.
Scientific bias -- the idea that hard science always proves things conclusively (examples: the debate on global warming, or that butter is healthier than margarine).
Confirmation bias -- we seek out information consistent with what we already believe, and ignore or disregard information that challenges what we believe.
To those of you who think you can control for these biases (or more laughably, to those of you who think you don't have any biases), I'll say this: The most dangerous biases are the ones we think we don't have.
Finally, for a surprisingly balanced discussion of media bias, as well as quite a few hilariously embarrassing stories about famous newscasters, I recommend Bernie Goldberg's excellent book Bias. It will change how you consume the news.