There's substantial literature out there on the subject. But of course finding it without it ever being noticed that you went looking for it might be tricky.
If dL feels like it, I'll leave it to him to explain the whole idea of the "social graph" in comments. The simple version is that unless you are very careful (and probably even then), everything you do online leaves traces. Even if you didn't use the Internet to get that secret NSA document to that reporter, there's a good chance that things you did online would constitute "tells" that you were interested in doing something of the sort.
So, to protect people who are thinking about doing things that should be done but that could get them in trouble, the information on how to do those things needs to become so ubiquitous that seeing them won't produce a blip on the "social graph." That is, it needs to become difficult to AVOID learning how to set up a dead drop, hand something over with a brush pass, or create a one-time pad without using a computer. The blogosphere, forumsphere, etc., needs to be positively dripping -- polluted -- with that information, such that someone does not automatically become a "person of interest" for having been exposed to it.
Today's retrograde tradecraft tip: Start making a habit of forgetting your phone when you go out. Not every time, just fairly often. Create some ... randomness ... in your social graph. Think of it this way: If you religiously carry your phone -- which is a tracking device that keeps track of where it is at all times -- then leaving it at home the one time you'd rather not be tracked might be the equivalent of sending up a flare. "Alice is gone from home from 1-5pm every day without fail -- except the one day that this suspicious thing happened, her phone says she never left the house." But if she forgets it once or twice a week, well, hey, Alice just has a tendency to forget her phone sometimes and there's nothing suspicious about her doing so on a particular day.