Whenever I come up with story ideas, I usually have a mental image of the story’s characters as well. For example, my characters are usually famous people. In the novel I’m working on now, my protagonist would be played by Mila Kunis, and my antagonist would be Johnny Depp.
Why bother casting a novel if it hasn’t been made into a movie yet? Because visualizing your characters as they would actually appear in reality is fantastic.
Take a minute to calm your mind. Breathe in and out. Focus.
Now, I want you to imagine the world of your novel. Unravel the setting, the landscape, and the time frame. See the buildings, trees, and streets in your mind’s eye. Next, move on to your characters. Imagine them going about their everyday lives. Who do they look like? Pretened you’re watching a movie adaptation. Which actors come automatically to mind?
Once you’ve come up with some famous names, do a Google image search to find some photos of them. You can save them to your computer for reference if you want. Now, whenever you get stuck on a difficult scene, imagine the actor in your character’s predicament. Picture him or her in as much detail as you can. What does he or she do in that same situation? What does he or she look like? What does he or she say?
This exercise has proven useful to me, but it might not work for everyone. It’s been my experience that visual learners and writers with a more visual sort of memory have a better time with this technique, but feel free to give it a shot, no matter what your style.