Ideo University offers a class called From Ideas to Action. The class teaches six ways to prototype. Here are two of my favorite prototyping methods.
Create a Story: Tell a story or create a storyboard that shows how your idea solves a problem. Through the story, people experience your idea as if it were real.
Write an Advertisement: Create an advertisement or a brochure that promotes the best part of your idea. I've written brochures for training programs that excited people and provided valuable feedback.