Hello.
First of all, before turning a novel into a script, you should know how to write a script/screenplay. Here is a helpful site with all you need to know:
Screenwriting.info: How to Write a Screenplay
Next, give whoever is writing the screenplay your novel. Let him/her read it. Now, with transforming a novel into a screenplay, a lot of things from your novel have to be omitted (for time purposes). Most movies last anywhere between 1 hour, 30 minutes to 4 hours. So, depending on the length of time, I would have him/her include the major parts of your work, and allow your screenwriter the ability to add/delete scenes, and made it interesting. As with most movies, they'll be too long if you make the ENTIRE novel the movie - keep your viewers' interest, and you help to decide what to keep/omit.
Good luck. Screenplays are a pain in the neck, but once you know what you're doing, you'll be fine. Happy trails!
