Overplanning! I plot everything in detail before I even start to write, so I already know how many chapters I'll end up with and what will happen in each one. I'm an overwriter too, so word count-wise, I usually have to keep a max limit in mind as regards what I can get away with in my genre, and then work out roughly how much I need to allocate to each chapter. I know full well that I'll hit or go over that limit on the first draft, and then it's all about ruthless editing to chop the thing way down.