You’re a Writer. You Can Write Anything.
Start with this mindset: you’re a writer. You can write about anything, because you can communicate. Few people communicate well, so be proud of yourself.
Freelance writers come in two basic groups: specialists, and generalists. I’ve always been pretty much a generalist. However, specialization happened, when I started to write consistently about several subjects, like technology, productivity, and business. Most freelancers end up specializing in this way. They write several articles about something or other, then they’re asked to write more. Before they know it, they’re a specialist in an area – they’ve become an “expert.”