Fine, I'll tell you guys how I form my opinions.
I generally don't trust the German media enough to be able to draw my information from one single source. When I say that, I really do mean information, as in, reported facts. I read media watchblogs a lot, and what I have seen exposed over the years has completely disillusioned me, leading me to doubt virtually every fact that is reported. So what I do, if I really feel I want to be informed about something, I check it on several news outlets of which I know that they use different sources. If all report the same thing, then I believe it. With international news, I generally don't consult German media at all. Of course, experience has taught me that I can put some trust on certain outlets concerning certain things. But I keep being wary. For background, I only rarely read what is written in news media, but prefer to do my own backup checks. I have two major academic libraries and an entire internet at my disposal, after all. Incidentally, I don't watch TV at all.
So that's how I obtain information and facts. When it comes to forming my opinions, the first thing I do is see what columnists and journalists write in media outlets that have traditionally stood at the end of the political spectrum contrary to mine. In other words, I try to find well-founded opinions that I can expect to disagree with. I think that is the best test for my critical thinking. I almost never really read opinions from "my" political position, because I think that is pointless. I only do that when I'm at a loss to find rational arguments for or against something; ironically, that is usually when I disagree with those opinions, too.
So, you say, that takes a lot of time. Yes, it does. It takes a shitload of time. And I don't usually have that sort of time. My consequence is, that I don't have very many political opinions, because I can't found them properly. And of those few that I do have, only a tiny number are actually strong opinions that I would go out defending - mostly, I prefer to state them and see them discussed, ready to change them when I feel convinced.