It depends on the game genre... I don't have too much experience with visual novels yet.  Is it like an interactive comic book, with music and portraits of the characters? 
Showing your planned workflow and showing concept art or even raw pencil sketches could be a good start. If you have a more story-based approach, a few descripting words about the characters, or the story plot is OK (similar to a book's back cover text). Then as you move on, you can write in your Devlog or blog each week of your progress. Even small stuff counts, like searching for background music, or writing a character's personality traits. The main reason for Devlog is that we can see what you are working on, get excited :) or can give feedback or help you early, before you commit too much effort into your project. The community can help you if you get stuck in the technical parts too.