In regards to reading the WSJ, you're asking the right question. Personally, I think it will be most beneficial to you if you read articles that are short and articles that seem interesting to you, at least at first. This is primarily because you'll be more motivated to do it. As you improve your skills, you can start to read some of the more technical articles that you might have found too boring earlier in your preparation. These are usually found in the Money & Investing section.
The real key to cracking the difficult RC questions IMO is cracking the structure of every passage. This approach also mitigates the risk that you'll lose interest in the passage and as a result, lose comprehension. Basically, the way to crack the structure of a passage is to take very structured notes. The awesome news is that the GMAT sets this up for you on every single passage (at least every passage that I've read). Let me give you an example: every paragraph has a topic sentence and then has a few supporting points, and usually has a transition sentence. Sometimes, this structure is tough to isolate or maybe it's camouflaged by complex technical information, but it's there. You don't want to just write down details about the passage or even things you think are important. Instead, you want your notes to visually depict the structure of that passage, i.e.,
I. topic
a. point 1 (not the whole sentence. shorten the sentence down to the one thing that it's saying.)
b. point 2
c. point 3 or maybe counter-point
II. next topic
etc
The reason that the WSJ is so great is that articles in there are usually not as well structured as GMAT passages. Forcing yourself to structure their points will make it incredibly easy to do the same thing on the GMAT, even with the most technical passages.
In regards to the other advice in this thread, it's all good. Saga, in particular, is very correct in noting that the 700+ level questions in RC and CR are about deeper meaning. The easiest way to uncover that meaning is to take notes on all the passages you read. For me personally, I usually don't even refer back to those notes. Just the process of taking the notes will ingrain that info. When a problem is very difficult, the notes almost always uncover the answer. Arun is also clearly correct. That is the easiest part though. Just read a lot and you'll get better at context.