To position yourself as an expert, learn everything you can about a subject. Develop your knowledge: read books, attend classes, listen to your market, get training, attend seminars, find a mentor, join a mastermind group of like-minded individuals, watch videos, and study.
To position yourself as an expert, share your knowledge with others. Deliver presentations and teach others on your topic. Look what TED Talks have done for normal people who simply presented their passion and thereby launched careers, fame, and fortune. Interact with your target market. Maximize use of the Internet and SEO.