There are generally considered to be two basic approaches to writing fiction. "Pantsing" (short for writing by the seat of your pants) means you sit down with maybe just a basic idea and make it up out of nothing as you go along. "Plotting" (also known as "planning") means that you've planned the story out ahead of time, you have an outline of the events of the story and all the who, how, when, what, where, and why figured out before you start writing. This isn't an either/or thing; it's more like a spectrum, ranging from people who say they sit down with nothing more than a title or a character's name in mind and start writing from there, to people who have planned exactly what will happen for every 100 words of story. Most writers will fall somewhere between these two extremes. Which way is better? Neither. It just depends on how the writer's mind works, their comfort level with not knowing ahead of time what they're going to write, and, to an extent, what they're writing. For example, an intricate mystery novel probably requires more advance planning than does a stream-of-consciousness literary novel.
I'm more comfortable plotting. Not in extreme detail, but I do like to have a good idea of what comes next and where things are headed when I sit down to write. I'll start a novel with the beginning, the ending (or at least a general idea of how I want things to turn out) and most of the major and minor events of the story written down on notecards or as bullet points in a document. Things will change from time to time as the story details develop, but generally I know where I am and where I'm going.
But writing the first two books of the Daughter of the Wildings series has been completely different from this. All I had to start them was a basic idea of the first scene or two, and the basic premise. With the first book, I only had a vague idea of what was going to happen next through most of the story and I really had no idea how it was going to end, and the ending completely surprised me--for one thing, Beneath the Canyons was supposed to be a stand-alone novel, but the ending opened up more questions than it answered. Ta-da, instant birth of a series.
Once I had an idea of the general story arc of the whole series, I knew pretty much where Book 2 had to end up. And I had the first scene in mind (which now turns out to be the second scene). Again, I found myself stumbling from scene to scene not knowing what was going to happen next, and finding some surprises along the way. I wrote about some of them in an earlier post--Silas looking at some events and drawing a different and much more logical conclusion than the one I had planned for him to come to, and then the day when he pretended he had no idea what he was doing and then decided he did. (This was when the book almost got titled "Silas meets one of the awful fates from the 'apologizing to your characters for the horrible things you've done to them' thread on the National Novel Writing Month Boards".) Then the biggest surprise of all--when it came time to confront the bad guy, it turned out the bad guy wasn't who I thought it was!
So, a mix of panic with, "Hey, this could be really cool," and I decided it would work. And it does, and the ending is falling into place perfectly now. I don't understand why the books in this series are turning out to be so hard to plan. I don't like that mind-numbing, stomach-wrenching feeling of writing the last paragraph of what I know, and then trying to think of what comes next. But now that I look back over the story, I can see where, in the process of desperately trying to make things up as I lurched from paragraph to paragraph, I've done some really interesting things with the world, the characters' situations, and some plot threads from the first book. So, hooray.
This is why my plan is to have all five books (at least, I think it's going to be five) written before I start revising and releasing them. Since I don't know what's going to happen in the future of the storyline, I need to be able to go back and make adjustments to earlier books to match. But when it's done, you'll be able to start reading the series knowing that it's done and that the story isn't going to go off the rails right in the middle. The going off the rails will have already happened and been dealt with.
On another note, if you like the idea of a mixed-genre western with an unlikely couple as the main characters, I strongly recommend reading Camille Laguire's Mick and Casey stories: Have Gun, Will Play (novel), The Curse of Scattershale Gulch (novelette), and two of the stories in Waiter, There's a Clue in My Soup. Plus she's going to be posting a new Mick and Casey serial in March!