People in your field need to know how you think, and to be able to share what you have to say with others. But who's going to publish content from an unknown? Well, you are. Start a blog (Wordpress and Tumblr are two of the best resources for bloggers) and let your colleagues know where they can locate your brilliant opinions. Better yet, have them sign up to receive your blog posts on a regular basis. The power and ease of social networking will allow your “fan base” to spread the word that you are someone who's worth paying attention to. If you're not a good writer, find an editor who can translate your thoughts into good copy.
The next step in your quest to be “an authority in your field whose opinions people read” is to publish in someone else's publication. The publishing landscape has changed enormously in the past few years. When I began working in digital media in the early 1990s, we said that the Internet would change everything. It has. In publishing, that means it's probably not a good idea to expect to be paid to write. Consider it a loss leader—an investment that can create revenue-producing opportunities (consulting, a job, etc.).
You can begin by being an interviewee or a writer for a friend or colleague's blog. That can move you to being quoted as an expert by a well-known industry publication. The final step is to write a book. Trust me, nothing creates credibility like being a published author. Be aware, however, that you will probably have to self-publish. If you're Stephen King or James Patterson, then the big publishing houses will be happy to work with you. Your celebrity includes a built-in fan base. If you're not a “name,” however, then you self-publish. Think of it as another investment in your career. Being an author, you'll be treated with a greater degree of respect. That's been true for me. In my field, however, title really matters. So I decided to get my doctorate before my first book was published so the cover would read “Dr. Austin.” You'll need to decide what's going to work in your industry.
I'll add a caveat to this tip: If you don't write well and can't find an editor, don't go this route. There are other ways to become an expert in your industry if writing is not one of your strengths. For example, if you're opinionated and well-spoken, you can be someone other writers contact for a pithy quote on a regular basis. It'll be your words—but someone else will have done the writing for you.