I've described plot as a tapestry before, because it is. It's a big mess of intertwining plots and subplots that, with some rearranging, create something beautiful.
But like a tapestry, plot requires a lot of work. You can't sit down and type "Chapter 1" and then write an entire story without any rules or direction until you reach "the end". Sometimes that works, but most of the time it doesn't. What you have to do is weave your story into a coherent picture where every thread is where it's supposed to be. (Am I saying that you should outline? By no means. What I am saying is that the need to create a plot that works is universal to all writers.)
So how do we create a plot that makes sense and ties all the knots?
First, know your overall plot. Even SOP writers have to know where the story is going, to some degree. I usually know the beginning, the end, and spotty sections of the middle. I don't outline, but I do know my plot.
The plot must have some structure. In practice, pure seat-of-pants writing doesn't work. If your beginning has nothing to do with your end, you have a problem that needs fixing. Most writers find that structuring a novel with a definite beginning, middle, and end helps.
In most cases, everything that happens in the novel must be a result of what happens in the beginning, which is often called the Inciting Incident. OYAN requires a full outline, but it also requires you to know the dramatic turning points of the story: The Inciting Incident, Embracing Destiny, The Black Moment, and The Showdown. You may find it easy to just outline those sections and leave the rest to figure out as you go.
Here's a bit of advice from me: if you're writing in third person, stick with one or two main characters. That doesn't mean that you can't have other point-of-views. It does mean that the story is usually about the character telling it. Lord of the Rings is, arguably, about Frodo Baggins. The subplot of the main character should continue on to the end of the novel. If the beginning of the novel is about one person, and the end is about another, then do they really have any connection?
There's another aspect of plot that I think is crucial for every writer to grasp. Every major plot strand should have some kind of resolution. This is especially important with characters. There are a lot of characters in novels, but all of the "important" ones should have a resolution. That's a fun thread to play with: recurring characters give a sense of continuity and makes the novel feel less "random". If I introduce a character who has a name, I almost always come back to that character at some point, even if it's several novels later.
Like most writing rules, there are exceptions. In mysteries and suspense novels, for instance, there are purposeful "red herrings" that are meant to lead you away from the real direction of the plot and make it more unexpected.
Also, many small characters don't need to come back; the man at the gas station whom you ask for directions, the bored front desk lady at the local hotel, etc. However, sometimes small characters like these can help foreshadow something else. In The Thirteenth Call, the reader meets a character briefly—we don't even learn his name—that has significance later in the story.
Make sure that every strand makes sense and feels realistic. The first draft of The War Horn had a dramatic (or melodramatic) character change in a minor character that felt completely unrealistic. People don't change as easily as the novel supposed, so I changed that plot strand and tweaked it here and there for realism.
And lastly, use the plot to foreshadow something later in the story. Remember, the end must come out of the beginning. You can foreshadow almost anything: characters, character change, betrayals, plot, plot twists, danger, and even theme. (In The War Horn, the first inklings of the story's theme was introduced from the second page.) Use the little strands of plot to foreshadow something greater in the story, instead of leaving them loose.
In short: to create a plot that keeps things rolling, know and structure your plot, keep with the same characters, resolve plot strands, make sure the plot stays realistic, and while you're at it, use the plot to foreshadow too.
What do you think? What are some other methods or principles we can use to create a plot that works and doesn't wander around?
Let me know.