Many tend to search for information the CONFIRMS what they believe rather than INFORM what they do not know or a different point of view.
Bias is not just found in news reporting. Sometimes scholarly articles also fall victim to bias and articles will be redacted.
Be wary of any sort of bias or slant - political, religious, etc.
Are all sides of an issue represented?
Is the author affiliated with some organization that would have a vested interest in swaying your opinion?
Is the language calm and neutral or inflammatory?
Check for the author's organizational memberships - Southern Baptist? Nature Conservancy? the NRA?
Was the source created to inform you about something, or persuade you of something (including persuading you to buy something)?