I usually first ask myself if a story sounds sensational or not. That's step number one. Secondly, I check to see who is reporting the story and whether or not their story appears to be well sourced. If the story is being reported by a credible news agency like the Wall Street Journal, New York Times, San Francisco Chronicle, Chicago Tribune, Washington Post, etc. I tend to believe the veractiy of the reporting. If some obscure website that I haven't heard of is reporting something, I won't believe it's reporting unless a more credible, well-established news organziation is reporting it as well.