Overall, though, I like to have a pretty clear idea of the plot and its main markers -- something a little more concrete than just a vague idea that This is Where We Start and This is How It Ends, although in some cases I'd be happy even to have those two things laid out. It's frustrating to feel bewildered by your own story, uncertain how to make it all work. Hitting a roadblock on the way from Point A to Point B is bad enough, but feeling like there's a massive pothole (or two or three) that you can't seem to bridge and being unable to progress until you do bridge it (or them) is even more frustrating. The same goes for a vague story idea of which you have one or two elements, maybe a handful of characters, and...basically nothing else. This is when writers start to talk about "brainstorming." Sometimes they even talk about sitting down and brainstorming.
Confession time: I've never really figured out how this whole brainstorming thing works, and I am really, really bad at it.
I think best through the process of writing, and there have been a number of times when I have become so frustrated with a story idea for not taking shape or with huge plot questions for not resolving themselves that I have sat down with a pen and a notebook and tried to confront the problems head-on. I wrote out the questions that had hitherto just been floating in my brain: Why don't the characters just resolve their problems by doing X? (I've no idea.) What is motivating this particular character? (Don't know that, either.) I know this character needs to be involved, but how? To what purpose? What even is going on here? (Noooooo clue.) The problem with this approach, I've found, is that I end up with a list of the questions that are bothering me and no answers. Seriously, I've looked back at old lists from story ideas that are still embryonic and thought, "Yeah... I still don't know what to do about that."
"Sitting down and brainstorming" is also generally ineffective, since unless I am in some way incapacitated, I don't like just sitting and doing nothing but thinking. My mind also tends to drift, or to keep turning over the same questions again and again without producing viable answers; it's the same ineffective process as writing out the issues. Pinterest is a nice idea for "gathering inspiration," but a) I don't ever use writing prompts, because they feel too inorganic; b) I'm very picky about which images fit the world of the story, so I rarely see things that just scream "Wordcrafter!" or "Tempus Regina!"; and c) pictures don't go very far toward inspiring me with words, anyhow. At most they remind me of things I already love about the story. They don't tend to help me moving forward.
I still haven't come up with a great way to plot, but generally the most effective course has been outlining. I know I've already commented many times that I am a big fan of outlines, no matter what I'm writing; I charged into NaNoWriMo 2010* with nothing but the names of two characters and an idea that I'd be writing about the Barbary Wars, and while it turned out alright, it was not a pretty picture and I didn't like doing it. Since then I've been a little smarter, or at least a little more conscious of my planner bent: Tempus Regina was still an extremely difficult book to begin writing, but I made sure I started with several pages' worth of outline; with Wordcrafter I thought I wouldn't need one, it being a rewrite, but I've revised my opinion on that in the last couple weeks. (Translation: I was totally kidding myself. I need outlines. I need them so bad.)
Stumped by a number of points, unable to get resolution by writing out questions, I began by listing the plot points I was sure about in chronological order. Then I started on an actual, handwritten outline, filling in the gaps between those plot points and forcing myself to put something down even if I wasn't positive about it. This did lead to a number of question marks, but it also turned out to be useful on three fronts: it showed me that I actually have a clearer idea of where I'm going than I originally thought and reminded me of upcoming scenes I'm genuinely excited about; it got some clutter (useful clutter, but clutter) down on paper so that I will (hopefully) not forget it; and it forced me to make some choices in order to keep moving. Just writing down questions presents me only with the things that have been frustrating me; it doesn't allow me to put those questions within the context of the whole plot, or to see the elements of the story that will actually hearten me. Organizing all of my thoughts, on the other hand, lets me see the full story unfold -- even down to the minor elements of a scene I've already charted out in detail. It's the short hand of writing the whole story, and I find that more thoughts come in that process of tracing the lineaments of the plot. Even in outline form, the words can take you -- or at least they take me -- to unexpected places.
*Oh my word, how was it almost six years ago? That's not possible.
Tell me about your plotting process! How do you get past a roadblock in a story you're writing? Do you ever get a story idea that just. won't. develop. properly., and how do you coax it forward? I'm bad at it, so do tell!