I frequently talk to experts who initially believe that experts shouldn't market. But as our conversation continues, it becomes clear that the foundation of that belief is a misunderstanding of what "marketing" is for professional service providers.
Marketing your expert services does not mean following some rigid set of defined steps and cookie-cutter actions. Some experts advertise, some don't. Many experts send out announcement postcards, while others mail newsletters, and still others (to their detriment) don't make use of their contact list in any way.
Your most successful marketing actions will be the ones that play on your strengths. If you are comfortable speaking to groups, look into CLE opportunities where you could speak on your area of expertise for attorneys who work on cases that involve those issues. Offer to make a a presentation for a section of your local bar association.
If you are more comfortable writing, then write articles about your subject. They don't have to be published in a legal publication. In our “Google” style world, an article published almost anywhere (academic journal, association publication, online newsletter, etc.) can increase your exposure and enhance your credibility.
Sum and substance - focus on what you are good at and comfortable with, and marketing your expertise becomes much less onerous and, dare I say it, even enjoyable.
Note: Rosalie would have my head if I didn't remind you that everything you say, write and do can and will be cussed and discussed and used against you by opposing counsel.