Well, given a visual novel is all about its story, a plot outline would be appropriate. Figure out some more details about your project, flesh it out, and then make a thread about it. Use your imagination, and think about what you would want to see in such a thread. Remember that the thread is NOT for recruiting people to your cause; the thread is to show off your game and describe it. Recruitment may happen, but it doesn't count towards the worthiness of the thread.