The debate always rages whether it is better to outline or just wing it. Many authors complain that outlining stifles creativity and prevents the organic growth of their storytelling. Others (myself included) find that trying to keep track of a novel-length work without an outline leads to millions of subplots and no resolution to our Main Character's story.
The heart of the problem lies in a misconception about what an outline for a piece of fiction should look like. We've all learned the numbered/lettered/bullet-pointed outlines taught in high school. And for most of us trying to apply that framework to a novel idea seems awkward.
However, that doesn't mean an outline of your story is useless or impossible. We simply need to start thinking about a fiction outline differently than a non-fiction outline. Personally, I prefer to think of outlines as a road map. I highlight the route I think I should take, but make notes about possible detours and side-trips that may prove useful. Nothing is set in stone.
Writing an outline is a bit like writing a very rough draft of your novel, a pre-draft if you like. The outline shows you the most important points of your story, gives you some idea of its structure and helps you plot the growth of your characters. When you write the next draft you can always revise, adding material where it's needed and cutting out parts that are redundant or just plain don't work.
This “pre-draft” should help you organize your ideas into a cohesive whole so that when you begin the rough/first draft of your novel you can let the imagination run wild and not worry about forgetting some important point or that clever bit of dialogue that popped into your head whilst weeding the garden.
“All right,” you say. “I'll give it a shot. But how do I write an outline for a novel?”
Like pretty much everything else writing related, do what works for you. You might have to try a few (or a lot of) different things before you find the right method for you. And you may find that the “right” method will vary from project to project.
Here are a few ideas to help you get started.
Every plot point gets a card. Cards are then laid out in order from beginning to end of story. This is especially useful if you have ideas for scenes but no clear notion of which should come first because the cards are easy to shuffle. Additional notes can be written on the card as well. For example:
John Receives a Letter From Nina ← plot point
He realizes he still loves her. This is what prompts him to take pack up his stuff and go find her.
Write a page or five summarizing the story from beginning to end. Include as many details as you feel are pertinent. You might try a paragraph per chapter. Or a single paragraph for the beginning, middle and end, respectively. This method is good if you prefer a more stream-of-consciousness approach to developing your story idea.
Make a list of the most important points in your plot. Add points as necessary to fill in gaps so that the beginning of the story flows into the middle which flows into the end. Subpoints may be added to clarify more complex actions. In general, one action (or beat) should be one point. This method allows you to see the bones of the story very quickly and if you already have a good idea about how the story will flow usually takes only a very short time to write out.
There are other methods to be explored (mind-mapping, napkins, spreadsheets) but, in my experience, they are mostly variations on these three. Each method has advantages and each will appeal to different writers in different ways. I usually go with the bullet-point approach, but I've used both the summary method and the index card method as well depending on the situation.
A little bit of experimentation and you should find a method that works for you.