I’ve discussed outlining on the site before (just search through my Writing posts if you’re curious) and I’ve yet to settle on any one outlining technique that I use ALL the time. I find that different approaches work in different instances.
For instance, on the Paizo books I used very detailed outlines that went on for some 10k words. I’ve scaled that way back for the current books and right now it seems to be working. I think about the main arcs and threads, who’s in them, what the challenges are, and what happens when, jot that down to make sure I’ve got track of it, and then start drafting (this is AFTER I know who the characters are, what they want, and, particularly, what the villain wants).