They may have heard of you. They may have run across your name in another ad. They may have an old business card, one that you put out before you had your URL on it. They'll go searching for your name so make sure your name is a prominent part of your page and part of your registration. They look for answers and solutions.
People go searching either because they want the answer to a question or a solution to a problem.
Your trick is to figure out how they're going to think about that question or that problem and then base your registration on their terms. Probably the best way to get that we tell our clients is to find out what people ask about when they call your office for the very first time. That should give you an insight into the way they think about what their problem is. Here's a quick example. Some folks may go looking for the name of a particular real estate agent when they want to buy a house.