First, you should acknowledge that all sources are biased to a certain degree, some more than others. Any source that claim to always be "Fair and Balanced" like Fox News is usually anything but. When looking at a news article you should always ask yourself these questions:

1. What idea/agenda is the author/source trying to express?
2. Who benefits (monetarily or otherwise) from the expression of this idea?
3. Based on what you know, are there any contradictions in these ideas? (ESPECIALLY self-contradictions.)

Source reliability is only a small part of the equation as appeal to authority is usually overvalued:if Fox News says the Earth revolves around the Sun, that statement doesn't suddenly become false. To determine the veracity of an article is simple, but not easy: you can only derive the truth from hard facts. You should look at the primary source and evidences and ask yourself:

1. Are there any hard verificable evidence such as photos, videos, or other direct documentations?
2. Are there only unverifiable, anecdotal, and/or circumstantial claims and evidences for this?
3. What's the original source from which the claims were made?

This should give you a good framework of spotting fake news.