So, you need to have some profession for a character in your story--but you're not an expert on whatever. The September 2011 issue of Romance Writers Report (from RWA) has an article by Courtney Milan, "Five Ways to Fudge Legal Details". The author focuses on legal details, but her advice is good for handling any profession or job in your novel if you are not an expert in that field. This blog post is a combination of suggestions from that article and my own advice.
Her first and most important advice, which we know authors will ignore, is that if you have no experience with the legal profression, do not write lawyers; if you must write lawyers, avoid talking about the character's legal practice. I say the same thing applies to cops, chefs or chiropractors.
If you do have a character in a profession in which you are not experienced, you absolutely should have someone--several someones--who is in that profession read your book and point out the errors. Law and law enforcement are especially complex, as there are so many types, plus laws vary by location (state, city, federal). So get several experts, but make sure they are the right variety--if you write an FBI agent, don't expect a small-town cop to be able to give you the insider scoop on that job. And it can be very helpful to have consultants and beta reviewers who teach--someone from the police or FBI academy, a doctor who actually teaches at med school, the director of a beautician college, whatever applies.
Ms. Milan suggests, "Have your characters choose not to consult lawyers." There can be many reasons why your heroine feels that seeking legal advice would be too expensive or time-consuming or bring more trouble, why your hero doesn't want to involve the police and would rather investigate himself, or why your heroine doesn't trust doctors so decides to treat her symptoms with "natural" cures. That way you can avoid having to provide a realistic and true representation of that profession.
The last piece of advice: "Have your characters delegate". Not only is it easy to get the details wrong, but often those details are boring or are unnecessary for your story. Is the cop a central character, or can all the crime investigation details occur off-screen? Does the reader need to know the details of meal preparation in a restaurant kitchen, or just that the food was poisoned? We probably don't need to see the doctor's office or the medical procedures, we just need the results and how that affects the characters.
If you have something that must be handled by a lawyer, have your character delegate the matter to a lawyer. "You take care of the details," he said in a commanding voice. "Call me when it's done."If you present details in your story, they must be factually correct. But there are ways to avoid the details, fudge the facts, when they aren't critical to the story's flow.
Sometimes it really is that simple. [...] delegation means you have no details to get wrong, and no readers to bore.