I consider myself as having expertise in three key areas: employment consultant with 10 years experience, which advised people to writing, job search, interview techniques, etc., language arts, and public school teacher to resume reading, which I have nine years experience teaching high school students are from public schools in reading techniques, and finally as a photographer I have over 25 years experience, selling photos, pictures of adult education, and have the articles as well as having my photos published.
Of course I started writing articles about photography, but from time to consider the other two areas related to my own experience. If I could only give advice, if others agree or disagree, it would be to the area is considered to have some knowledge and to write with occasional excursions into other topics, if you feel strongly about them to choose.
This will take some time (about 5-10 years), before starting to be recognized as someone to turn to when the subject arises. This applies in photography. The big names in nature photography, that’s my genre chosen picture, specializes in nature photography for several years, even writing books, but if you ask them, they surely will tell you the same thing that many spent years before they were the only people she turned to her sex and picture appeared, though some of them pictures of other disciplines to make their lively hood from the main specialization.
I do not think there’s anything wrong with writing about different subjects, if all you want to do is write and maybe some money, but if down the line you want to be considered an expert, then the concentration must be that The area where you write with authority on his years of experience as your backup.