I see a music journalist as a music enthusiast who has the creative ability to voice their opinions in print, online, and over the radio. They will have specific tastes that will be the grounding for their choice of jobs, but will also be able to put aside interests and prejudices to branch out into other genres of music. A successful music journalist must be an expert in their own field but, in order to progress in their career, must be able to write about a whole range of topics that may not be of specific interest to them as a person. Starting out it seems to be very much who you know not what you know, so having the gift of the gab doesn't hurt. The ability to go to a venue and get yourself a free pair of tickets and maybe a meet and greet pass is a massive bonus. that way you can get the reviews to get you a job, for free. It also helps to know the doormen/press officers/house managers etc. as these are the people that will help you get to the places you want to go to.
