Need more than 1 credible source. Typically 3 sources.
get the other side of the story rule
get a complete picture, dont just listen to one source tell one side of the story. find more, and let them tell their viewpoint.
equal space rule
make sure each view has equal space in your story. dont be biased and focus solely on one aspect of the story.
equal access rule
Make sure that you are accessible to all sources equally. For example, dont avoid covering one side of towns stories because the reader pool there is low.