Many of these things could alert you to bias when watching media, but the easiest to detect would be the partiality toward a particular viewpoint.
If the media is only stating something from one point of view, rather than simply stating the facts or giving both sides of the story, they are likely trying to get the viewer to believe the side of the story they are presenting. They are being bias, instead of allowing the viewer to make their own decision based on all the facts.
Other things that can help alert you to bias, would be emotional words and images, inaccuracy, and opinons disguised as facts. While opinions disguised as facts, would definitely mean there was bias, it might not be easy to detect. Also, emotional words and images and inaccuracy might not mean there is bias, but it could mean the media is trying to compensate for something.
