Forget chapters. I learned during a previous project that numbering your chapters is the very last thing you should get around to doing, because you will add chapters in between, and if you're numbering manually, this creates a lot of extra work. This time, I spent so much time moving scenes around and having to deal with scene-specific chapter titles, that I'm amending my previous maxim. From now on, my outlines will be scenes, and I'll put them into chapters once I'm satisfied with the way they play. I'm tempted to say that I'll make exceptions for prologues and the like, but I doubt it. This draft has had three different prologues, as the story has grown in scope and it has become necessary to add scenes to the beginning.
Placeholders are awesome. When I was writing sci-fi, I would get stuck on introducing a character and having to find a name for that character. This time, the problem was MacGuffins. But I came up with something to call them knowing I could find/replace it out later and not lose my flow, and it kept me from getting "blocked" a number of times.
Have a good idea of where you're going before you get there. I started this story thinking it would be a short, intending to publish it as a Kindle Single (word length of 5,000 to 30,000). After about 10,000 words, I realized that this was going to be novel-length and began outlining accordingly, but my early chapters still have the jarringly brisk pacing of a short story. Long story short, I started this out based on an idea, figured out the story trajectory, and then outlined, and then wrote to the outline, but now everything I wrote up front is going to have to be heavily edited or completely re-written. I think if I'd taken more time to hammer out details before I started on narrative, or focused more on characters than on plot with those early writings, they would have been less wasteful. On the other hand, some of the more organic developments were quite satisfying.
Books are not films. I made the mistake of having a two-headed protagonist, rather than a protagonist and a foil. This is useful in movies where you have to communicate to the audience through dialogue, but this isn't necessary in a book because you have access to your perspective characters' thoughts. In films, the characters are assumed to know whatever the audience knows, but you can't get away with that in a book. Which means that any bit of information that one character discovered had to be communicated to the other, which necessitated a few "oh, this thing just happened" scenes. I'm making it work by putting more effort into differentiating the characters (which means hefty re-writing of early scenes, but what can you do?), but if I had to do it again, I'd have gotten rid of one of my protagonists. In future books, I'm splitting them up quickly so they each have their own storyline to hold up.
Have a real ending. I had an ending written and felt more or less unsatisfied with it because it was unrelenting in the way it set up for a sequel. So I ditched it, focused on the closure, let it be known that the bad guy was still alive, and left some questions open. But it ends, that's the important thing. Also, this way a followup book isn't beholden to the ending I write for this one, which means I have lots of time to change my mind about what happens in book two.
So, that's the debriefing. Incidentally, I'm going to need some eyes on this thing before I try to shop it around. I've already got a couple of alpha readers looking at it, but if you'd like to alpha-read (read as: "read a very rough draft") or beta-read ("read a slightly more polished draft"), send me an email.