When I tell one particular friend of mine that I scored an interesting assignment, he always asks, "So what are you an expert on this time?" I used that story when I gave a talk to the local writers group about writing for trades. Someone at that talk raised a hand and asked, "I'm interested in writing for trades, but I'm not an expert on a particular subject. What do I do?"
I think one of the great misperceptions is that the writer needs to be an expert on a topic in order to write about it.
The reality is, while it is helpful to have some familiarity on the industry you want to write about, in the end, your skill as a writer is most important. A good, engaged writer will learn and develop a handy working knowledge, but will never upstage the real experts. If you can show you can handle a topic deftly, editors will hire you.
When I first started freelancing, I looked at the subjects that interested me most, the things that were part of my every day life: parenting, fitness, marriage, women's issues, sports. Parenting and women's magazines are among the most difficult to break into because the competition is fierce. Now, I have published in smaller markets in those topics, but I haven't broken into any of the major ones yet.
Someone suggested I try the construction magazines because I worked with construction people in one of my jobs. I never lifted a hammer, but I did learn to make conversation with people in the industry. I mentioned that job in the letters I sent out, and it landed me assignments. I tried the same thing with engineering. Heck, I live with an engineer. I know lots of engineers as friends. So I targeted engineering publications.
Engineering took me in the direction writing on technology. Construction steered me toward sustainable living. Now I've moved toward science writing.
If you knew me well, you'd think these are the least likely of topics that would be my writing niche. But I found that writing topics that go against my personality make me a better writer and reporter. When I write on a topic I'm passionate about, I struggle to avoid throwing my opinions into the piece.
Writing what you know can be good. Taking advantage of your life experiences can lead to a rewarding career.