I've probably talked a lot about this before, since it's been driving me nuts lately, but I try to explain often that I don't really believe we have access to the Truth very often (but we're always looking for it). This is most frustrating when you run up against two completely different explanations for something. When trying to school oneself in politics, it becomes apparent pretty quickly that there's a lot of competing and contradictory information out there, and at some point you have to ask with whom the truth lies (haha.... pun).
I think at a high level, it depends on the situation, and each issue should be evaluated separately. This can be a pain in the ass so my decision has been to find a source I trust and research what I can when I have time but generally accept what they say. If you don't find someone whose analysis you trust, but you still search for knowlege, you're just going to drive yourself insane.
Most of us have a source we trust. For many right-wingers it's Fox News. For moderates perhaps it's The New York Times or NPR. For me it's Socialist Worker. From what I've discovered on my journey, there are some useful steps to finding someone to trust:
Look for a source that shares your morals and desires.
Ask yourself what they might have to gain from printing inaccuracies or misleading through omission, spin or specific language.
Find out what sources they use, and if you find those sources to be trustworthy.
For me, I trust Socialist Worker because the people who write for that paper share the same morals and goals with me: We are against bigotry, oppression, imperialism and poverty, and for the idea of putting people before profit. I personally believe that they have nothing to gain from misleading the public (it would only hurt their cause), because if they achieve their goal, everyone in the world will benefit. They do use loaded language, but since I agree with their cause, it doesn't bother me.
I also tend to trust NPR because it seems like a reputable and largely neutral source, likely do to its funding by the public rather than corporate interests. I also get a lot of my news from The Guardian, a british newspaper that isn't afraid to comment more bluntly on United States news (it may however, be not so great for British news).
I don't trust sources run by bigots of any kind, because we don't share the same morals or goals. In addition, information motivated by hate is often even more colored by biases and intense emotions, so you end up with really dumb stuff like "Feminazis are Jews" (go ahead, google it). I haven't yet figured out if something motivates people to spread misinformation for their cause or if they just see what they want to see. These warnings apply for everyone of course.
In any case, I mistrust most mainstream news because news outlets like Fox, CNN, The Washington Post, etc are companies - they don't exist to inform the public, just to make money, and a lot of people have interests in this success including many people in government. Media and government have a mutually beneficial relationship. I think this is becoming common sense among people now, but it seemed very much like a conspiracy theory for the past 8 years or more. I think a lot of people assume people in government and media are just like us, clueless. I personally don't believe that.
So we're all going to come to different conclusions based on our own experiences, beliefs, and biases. I'm sure there are a lot of people who think that Socialist Worker would benefit from misleading the public because the people who run it want to turn the world into marching formations of grey uniforms and want no one to have choice and want to kill a lot of people. I personally don't believe that. :)
The other step to moving um, closer to the truth, is to get as many perspectives as possible. For most people (perhaps unless you're Noam Chomsky or something), your first impression is going to be missing a lot of pieces. As a radical leftist with a socialist perspective, I make sure to read views that I tend to agree with, but in order to get any context at all I have to understand what the mainstream media is saying. That way I can compare the status quo storyline to the radical storyline and ask which makes sense.
This process became really apparent in the past few weeks as I've tried to school myself on the Israeli-Palestinian conflict. I tried to understand it a bunch of times in the past and I just couldn't get my head around it for some reason (mostly because I couldn't remember who the Israelis were and who the Palestinians were - pretty dumb huh?). My first impressions came from hearsay and the mainstream media. What I heard was that the terrorists in Gaza, Hamas and normal people, were shooting rockets at and killing Israelis, so Israeli responded. Shamefully I have to admit, at this point I still had some inkling that "that's just how they are in the Middle East", because that's what I've been told my whole life. People are poor, and poor people are more prone to violence, and everyone over there hates everyone else because they're a different religion. I never really realized how little sense this made, and while I still think it's true for some people (it's no different from thoughtless and hateful racists and such over here in America), I don't think it's the rule any longer.
Looking at the socialist perspective (and even the regular left perspective like from the documentary Peace, Propaganda and the Promised Land) really made things make a lot more sense. Israel occupied Palestinian land tens of years ago, kicked people out and forced them to live in horrible conditions for years, so a ruling power called Hamas retaliates by firing crappy rockets that have killed very few people. Israel responds disproportionately and kills over 1,250 Palestinians (so far) not just out of racist Zionism, but because they are imperialist and because the US supports and funds their bullying in the Middle East. That's obviously not even half the story but it makes a lot more sense than the idea that Israel was defending itself, or that all Middle Easterners just like killing eachother.
So find a source you trust. Find a perspective and an analysis you trust. Mine is the Marxist analysis. Make sure to compare the mainstream story with your trusted perspective and ask yourself what actually makes sense. It's amazing what idiocy they'll try to stuff down our throats and we simply accept it because it's repeated and supposedly spouted by professionals (remember "the terrorists hate our freedom"?).
Of course, I'm not an expert on anything except attempting to learn.