Do you passionately want to take photographs of a particular subject? If so you possess the first and foremost requirement of a photojournalist! (It's no good to just wander around with a camera and hope you'll come up with something good.) It goes without saying that you will also need superb people skills and a knack for self-promotion.
If you love photography you will have studied it in your spare time anyway, but it is essential to borrow books from the library and visit galleries, because most internet resources lack intellectual rigour and have poor production qualities. Regardless, there is some good stuff online too. One example is the work of Robert Appleby, whom I believe is a British photojournalist (though I think he lives in Italy). Study every photograph in all of the PDFs on
his site. They are all superb examples of the importance of light and perspective in powerful documentary photography.
By the way, Mr. Appleby posts on the
www.photo.net forums under the name "
Another Bob". If you have some time to spare, it would be worth registering to trawl through some of his posts there to get an insight into his mentality. (His posts will show up on his member page if you are signed in.) He's a cynical old bastard, but amazingly astute and succinct.
Photo.net is probably still the best place to learn about photography on the net. Some of the world's best photographers - including some Magnum members and National Geographic staff - post there at least occasionally (usually under their real names).