Some article writers choose to write news articles, and some prefer to write about their own lives. The vast majority of article writers do not stick to one category, they just start writing an article about whatever they can think of, and this can be slightly detrimental to the Google rating.
You see, Google have all sorts of algorithms that help them to provide the best quality search results to their customers, and one of them is about specialization. Google will favor an author who has written all of his articles about science, rather than someone who has just written a couple.
Even so, there are also other algorithms which allow you to compete, such as keyword percentage, title choice, incoming links, and location, but you should still try to avoid writing about topics with no apparent connection. I started out writing articles about everything from the origins of the universe, to recipes, handy hints, commentary on society, as well as original music, and video guitar lessons, but now, I am trying to start writing articles within categories.
The thing about writing articles, is there is so much to it, from all the different paid article writing sites you could join, to the SEO needed to get your article on the first page of a Google search, to all the different things you could write articles about, and why those topics would get you more traffic.
There are two schools of thought in article writing. Try to write about the latest thing that anyone around the world might be searching for, and get a whole lot of immediate traffic, or, try to write about something that will be searched consistently for years into the future, generating you a steady stream of income.
Personally, I prefer the last idea, as I want my income to increase over time, the more articles I write, although, if you did make lots of money from current affairs articles, you could always put it in the bank. I recommend trying both ideas, but if you are going to write in different categories, why not try writing articles under a different pen name, on a different paid article writing site.
My favorite one at the moment is Bukisa, but I also write on Triond. I have tried a few others like Ehow and Helium, and you may want to try a few different ones, or even keep writing on a few different ones, especially if you want to write about the same individual categories consistently.
If you are writing on a paid article writing site that uses Google Adsense, remember that people need to click on the ads on your article in order for you to make any money, and the ads are based on the keywords in your title and article body, so you should try if you can, to write about keywords that both get a lot of traffic, and also pay well per click.
Try checking out the Google keyword traffic estimator, and just test out a whole bunch of different ideas, and see what makes you the most money for your articles. For more information on improving the SEO for your articles, by making links, using the right keyword percentage for every paragraph etc, take a look at my Facebook page: Writing for profit, where you will find all the best information on how to make money from writing articles online.