Consider the source. Is the person making the claim credible on the subject matter? Determine if the source has expertise and has demonstrated it in the past, whether it's an anonymous commenter on a news site or a university professor. Does this source have a track record of distributing correct information? Ask about the source's reputation.
Check other sources. There are several sites that attempt to get to the truth on certain issues. Snopes.com delves into a wide range of urban legends and political rumors, while politifact.com focuses on politics. Some false rumors continue to resurface, such as soda companies leaving out "under God" in packaging that includes the U.S. Pledge of Allegiance. Sometimes those rumors are verified as true. On political sites, pundits take issue with the credibility of those doing the fact checking and claim bias, but a wise news consumer has enough information available to check the facts independently.
Check for bias. If a source's presentation gives little attention to possible counters to a conclusion, it's a good indication that more investigation on the subject is warranted before that conclusion can be believed. It may be that the source's conclusion overall is correct, but context is always worth examining to arrive at an answer that satisfies the question of credibility.
Determine the intent of the information. Is it meant to inflame? If so, that is certainly call for checking other sources. Even if the information is presented as fact as a presentation on statistics, it is always worthwhile to consider other context. Most news stories are meant to provide information that will be either just interesting, new or will challenge longheld beliefs. By reading the tone of the message, there can be some determination as to whether the credibility of the information should be more or less suspect.
Question the listener's biases and perceptions. Information is received through the filter of the receiver. Therefore, it is important for someone interested in the truth to question his own biases in hearing the information.