Sometimes it’s good to just take a break from typing out your novel. Just because you’re breaking, though, does not mean you must mentally abandon the story which is probably starting to rule your life (and your dreams even). When you’re writing, it may be a good idea to get out a sketch pad and pencil and just sketch elements of your story, whether they’re characters, vehicles, or locations. This is especially true when it comes to fantasy and sci-fi.
Now, don’t worry if your artistic skills are somewhat limited. Mine aren’t by any means perfect. It doesn’t really matter, as long as you can get an idea down on paper. You can always develop the idea further, which will give you great visualization help when daydreaming and writing. In some cases it is very helpful to get on the web and look for inspiration. This is especially useful if you’re trying to visualize scenery and landscapes, and may help greatly when it comes to designing weapons and tech.
I often enjoyed drawing stuff from my stories, and sometimes I would draw something before I actually put it in the story. Maybe this idea will help your creative process. You never know, so why not try?