Tim Robbins in Robert Altman's The Player: Be careful what you wish for.
Occasionally, someone will approach—if that's the word I'm looking for—one of our authors about making a movie of their book or life. When you sign a contract with Lantern, you usually assign all your subsidiary rights—those are rights to your work should they become dramas, radio plays, movies, documentaries, etc.—to Lantern. We act as your intermediary and we split 50/50 any money from the purchase of those rights. Of course, as an author, you can "retain" any of your rights before signing the contract—preferring to negotiate them yourself or hiring a professional to do it. And some authors have done that.
Now, the distinction I made in the first paragraph between your work and your life is important, because the contract you sign with Lantern only concerns your book. If the person making a film or writing a play is only using it as background material and the creator is looking for a bigger story, etc., then that's beyond our publishing purview, and we'd recommend you get an agent to handle the remainder of the transaction. If the enthusiast, however, is interested in using language in and the story of the book, and you've signed our standard contract, then that's our business and where we advise caution.
Many people have their books "optioned" (i.e. the rights bought and sums of money exchanged) and the buyer fails to sell the idea to a movie studio or production company. The result is that your book languishes unmade—without anyone else having the chance to buy the rights. That's why I'd recommend making sure the buyer has more than just a dream, but has a production company interested—if not invested—in the project coming to pass.
This is where you, the author, need to be smart, because there's a lot of flimflam in the movie business, and you can be promised the world (and even in the case of one author, given a car) and still your book doesn't get turned into a film. Meanwhile, you've spent a lot of emotional and physical energy on the dream of a movie about your book, and nothing's come to pass. So, make sure the would-be filmmaker is reputable and has a plan.
One final thing, you may be flattered by being asked to be the screenwriter, or treatment creator, or being very involved in the project. Think carefully about whether you want that to happen. It may take up a lot of your time and lead you away from your real goals. In short, be cautious, ask around to check the individual's bona fides, ask them what they've done with your work, and how they've going to get it made. You may even wish to hire a professional rights agent to handle the transaction. It may save you a lot of grief in the meantime.