Personally, I look for falsifiable facts, especially numbers. Even though the NYT is heavily biased, if it claims “X people died as a result of military activity in country Y during year Z”, I believe the number is approximately correct, although you have to look carefully at the wording. Now, of course, I also know that the NYT will simply omit facts that are inconvenient to the view it’s trying to promote.

So it could be said that I “trust” the NYT, AP, etc, to not commit lies of commission, but I don’t trust them to avoid lies of omission.

When it comes to getting a full picture, the most common strategy is to check with both sides. E.g., I trust Fox News to give a (mostly true) list of facts damaging to Democrats, and NYT to do the same for facts damaging to Republicans.

“Trust” implies a faith in a source’s morality. That seems foolish. Instead, it would be better to look at self-interest. Media sources that want to be taken seriously can’t outright lie, because they would be caught, so their main tool of distortion is omission.

There is a quote I can’t find from a Russian expatriate during the Communist years who was asked where he got his news from in the USSR. He said that he got news about Russia from Radio Free Europe and news about the West from Russia, because countries lie about themselves but tell the truth about others. To this day I occasionally find seemingly outlandish assertions made on RT about something the US has done that actually turn out to be true.

The more interesting question:

> How do we decide who to trust when we enter an arena where we have no prior understanding and no context to help us know what’s true and what’s false?

This is epistemology and cognitive science. The main answer is that we have to find sources that consistently do not conflict with what we already “know” to be true. For instance, if a “scientific” source tells me DNA doesn’t exist or evolution didn’t happen, I would immediately write it off. But of course as you say, how well this method will work depends on the accuracy of what we already “know”.

The other test of a “good” source of information is if it can generate useful predictions. If source X tells us that a war in country C will result in good things, and source Y says the opposite, and then we enter that war and bad things result, then the credibility of source Y should go up and X should go down.