Pre-production is a process of planning one's film and includes, research, brainstorming, short story/treatment, character sketching, script writing, and more. Celtx is an indispensable pre-production tool. While it is most famous for its screenwriting tool that properly formats one's script according to industry standards, it is fairly comprehensive, providing storyboarding features, character sketch forms, treatment (short story) field, and more. Below is a 30 minute video tutorial that, while a bit dry, is highly informative and provides a solid training for Celtx.
Archive Hollywood Scripts