Good advice for starting a light novel?

[Froge]

Clearly we have different definitions of preparation.

After getting the concepts down (eg. character motivations, x to y, etc.) in my head, I will spend some time enacting out entire story scenes in my head with exact prose and dialogue, because I just can't resist the creative urge. Then when I actually have the opportunity to write that scene down I suddenly become bored because I've played through it so many times in my head already. This is pretty much my definition of preparation.