My planning varies manuscript-to-manuscript at this point, partly because I don't always have a lot of time to plan ahead of time. I would love to have a detailed outline before I begin a project, but at the same time I don't ever want to let that prevent me from starting something. (I try to plan my next manuscript (and other future ones) while I'm drafting my current one. However, if I finish drafting one project, I'll usually start to draft the next one within 24 hours if I'm not writing short stories.)
It's also hard to describe because outlining tends to be just one piece of my planning process. Usually by the time I get to an actual outline, I already have the whole story, so I'm just sequencing the events and then seeing if I need any additional events.
Before I can start writing, I need a beginning and some rough idea of the ending. If I haven't worked out a lot of the steps in-between, I'll write a few chapters to see how things are progressing and then just outline the rest of the book at that point.
I tend to think in terms of events, which I then might break down into scenes (although some events are already scenes). My planning of events comes down to what makes sense in terms of story progression, with an eye towards escalating stakes and tension.
The outline itself can look like anything. Sometimes it resembles a very long synopsis, sometimes it's bullet-points with sub-bullets, or bullets with a detailed description, etc. However, other parts of the planning document tend to look more consistent, since I'll usually start with a premise, followed by a longer blurb. Then as I'm drafting, I'll update the planning document with details so I can keep track of what I'm doing.
The one thing I try not to plan as much is dialogue and certain elements of characters' personalities, which I'd rather have emerge as I write so they feel more organic (which I think was a piece of advice I originally got from a Sanderson lecture).
In general, I see outlines as living documents. They're a writing tool, and I need to use them in a way that makes sense. I'll often make a few changes to my outline as I go along.
The biggest pitfall I've found in plotting -- in the past, anyway -- was that it contributed to procrastination, which is what led me to just jump-starting projects and working out the outline afterward (although I'll still have a general plan, and an outline for the early events). Plus planning can get overwhelming at times.