When I wrote my first draft, I didn't outline at all, I just had an idea for the first time in years and I vomited it all out on the page over the course of a couple months before there could be any chance of slipping back into the non-creative abyss.
So, outlining was not something I did, or something I really knew how to do. As I began editing it into some kind of coherency and cohesiveness, I've tried several different things.
I've done query practicing on many occasions, to try and nail down what the character wants, what's getting in the way of that, and what the character will do to get it. I've written multiple synopses to try and clarify all the relevant plot points for myself.
I've worked through Shawn Coyne's Story Grid method,
here. I've worked through K.M. Weiland's character arc series,
here, as well as some of her other plotting and structuring series.
When I begin a chapter, I start with a few notes at the top of the document, sketching out what I want to accomplish in this chapter, what my character wants to accomplish, and any other details I want to keep focused on or don't want to forget to include (otherwise I tend to wander).
I've also gone to the end and worked backwards, chapter by chapter. That's something that seemed counter-intuitive at first, but I don't think I could have ever figured out how to connect the first part of my novel with the last part without trying that.
All of these things were helpful in different ways. I think outlining is something you have to learn, no matter which method you find works best for you. I'm a hands-on learner, so for this novel at least, outlining is something I have to do as I'm writing, rather than before. Next novel, hopefully I'll be able to do more of it up front.