Is this a new and unfamiliar source? If it is known, trusted, and reliable, it's probably OK to continue. If it's not, then it's important to pause and think about how to fact-check this information.
What can you find out about it elsewhere on the Web? Even a quick search to see what other sites say about this source can be helpful. Wikipedia can be especially helpful for this kind of investigation.
Is a known, reliable source covering this topic? If you are uncertain about the reliability of a found source, look for information on this same topic, event, or issue that comes from a trusted source instead.
Can you find the origin of this information? Every time information is reported by a source that's not the original, there is a chance that it could be misstated or misrepresented, accidentally or deliberately. Going to the original source is the best way to find information that is complete and unaltered.
(Adapted from Mike Caufield's Check, Please! Starter Course)