I'd like to thank Amie McCracken for giving me this idea. Actually, she made a comment on Twitter yesterday that reminded me that as I TRIED to drift off to sleep on Sunday night, I'd planned this post. Here goes:
Writing an outline is very similar to writing a synopsis, minus the head-trauma. Terry Wright, the Contest Chair at RMFW, has a very handy PDF on how to write a synopsis (this one is specifically for their contest, but the basic rules apply, just shorten it from eight pages to no more than four). But it's handy when you want to start an outline! (A note: if you don't read the PDF, you might get a bit lost as we move forward.)
So my method, and the one I recommend, is to start with the 5 Ws mentioned in the PDF. Pick out the one or two (try to limit it there) character(s) who play the protagonist(s) in your story and fill out the each of the 5 Ws. Then do the same thing for your antagonist. This is crucial because without this reminder at the top of your outline, it's easy to get lost!
Next, divide your book into five sections (or acts). Using the 8 Elements of Story, I divided my story up this way, but the actual divisions are up to you:
Part 1 (Character Introductions and Inciting Incident):
Part 2 (Rising Action and Rising Stakes):
Part 3 (Turning Point and Black Moment):
Part 4 (Climax):
Part 5 (Resolution):
After I got those typed up in my document, I started a new paragraph below "Part 1," and typed "Chapter 1." Then I summarized what I wanted to happen in Chapter 1. Repeat those steps for each chapter, making sure that you keep the 5 Ws in consideration! This is a great opportunity to figure out exactly what you want your protagonists to do, how you want them to do it, and what their motivations are. And if you find that something doesn't work structurally, then you only have to rewrite a paragraph or two instead of and entire chapter!
Keep that in mind, as well. I heard once (and I'm paraphrasing) that your first idea is your worst idea. Be prepared to THROW IT OUT! You don't have nearly as many "darling" scenes that will have to be butchered if you're prepared to make changes in the outline... you know, before all of the HARD work is done.
That's it. It may be time-consuming in the beginning, but it gives you direction at ALL times. And feel free to divert your path a bit as you write the book. To keep things easier for yourself, note the changes you make to the plot in your outline, that way, when your book is done, you have a document that only needs to shrink a bit to turn it into your synopsis for querying!
Have fun with it, too. This is a story that you're crafting. No one ever has to see it, so don't be afraid to make plenty of "mistakes" as you go.