I have heard a lot of different takes on the need to prepare an outline when writing a novel. Joe Konrath has said he spends a full week preparing a 40-page outline. Robert J. Randisi, who has written over 500 novels, doesn't use them at all. M. Louisa Locke adopts a more nuanced approach.
Since I'm accustomed to a task-driven environment, I find that the outline is somewhat helpful while writing anything longer than 10,000 words. Here are 5 tips that I've found beneficial to speed up the writing process and to get my own ass in gear:
1) The Initial Brain Dump - In the last few months, every idea for a novella/novel has come to me while on my commute to work. My neighbor takes me on the back of his motorcycle every morning to the BTS station down On Nut road. For some reason, this harrowing 15-minute journey every day through Bangkok's notorious traffic really stimulates the mind. So that I don't forget what I thought about, I try to write the major theme and idea of the book, the motivation behind the protagonists, and how the story will end on my iPad as soon as possible after the commute (usually on the 10-minute Skytrain portion of the morning commute). The entire idea for a novel comes to me in about 2-3 minute bursts. Of course, every schmuck in the world has "great ideas", but it takes hard work to turn ideas into something tangible that others can enjoy.
2) Character Development - Since no one likes one-dimensional or inconsistent characters, I keep a separate Word document with all the major characters and their attributes and flaws.I list their names and qualities to maintain continuity during the writing process and indicate whether they have some kind of secret that needs to come out later in the book. Typically, I just list two traits and the characters name (e.g. one of the secondary characters a novella that I'm working on is just listed as "Intelligent, but Naive")
3) Chapter by Chapter Outline - I've heard that you shouldn't worry too much about word count and that you should write as long or as short as you need to. Unfortunately, I need clear objectives and guidelines, and I can't just get the muse in me and start writing 10,000 words a day like some writers can. Therefore, I usually lay down each chapter and what the major plot points will be for the protagonist, and I estimate what the word count should be. This gets built from the Initial Brain dump. By having a clearly defined agenda, it helps me stay on track and make steady progress.
4) Scene Setting, Metaphors, and Zingers - Once in a while, I'll have a great idea on a metaphor or a snippet of dialogue that needs to go into the piece somewhere. Since I'm a very forgetful person, I make sure to write it down into the outline.
5) Keep it Fluid - Despite the estimated word count and chapter breakdown, I try not to be too restrictive with the outline. The content of each individual chapter is pretty open, and the Chapter by Chapter Outline just lists the big ideas and tasks that the characters have to accomplish. I've found that not being too specific in the outline allows the story to flow better and be more exciting.
All in all, the outline ends up being only 2-3 pages. Now it's just a matter of finding time to turn the damn things into a real story instead of just a bunch of notes.