Want to be a video game journalist? I'll let you in on a little secret. Even professional video game journalists don't know how to define “video game journalist,” because we do so many different things. We're reviewers, critics, previewers, live event reporters, bloggers, interviewers, and columnists. If you want the gig full-time, you should be prepared to write all of the above.
Most outlets have plenty of established writers to fulfill those roles, so it can be difficult to break in writing this sort of material unless you already have connections. There's one kind of games writing that's always in demand, however: features. If you can consistently write solid, well-researched features with unique angles, you will find work in this business, and once you have a reputation as a dependable feature writer, it's just a matter of waiting for the right position to open up.
So rather than give you vague advice about how to do the whole job, that no one is able to define in the first place, I'm going to tell you how to get into writing features. If you can jump that hurdle, you'll be well on your way.