The "don't plot" thing is something that I really struggle with. I think that one of my strong points is to be able to have a strong idea of what's going on, and then be able to easily and instantly discard that as soon as necessary - fighting for your version of what you think the plot should be just leads to unnecessary complication and argument - but it's still my natural inclination to explain stuff, instead of just digging back into character. And even when I'm falling back into the mantra thing in my head ("I did wrong before, but I'm going straight from now on."), it feels like it still comes out as just talking about past plotty stuff. ("I spent fifteen years in prison! I saw a lot of things in there! Let's talk about how that happened, and what's going to happen next!") Anyway, at least I'm cognizant of it - it's just a matter of beating it out of myself, I reckon.
Yeah, I caught myself introducing the high-class party in my first scene in the second run -- "Crap. Plotting. Must... stop...." It's weird that I've done improv for so long, and I still can't get myself to just hang out in character and see what happens. I think I got closer to that goal in my cop scene with Troy from the first run.
That said, it's cool to have something new & counterintuitive to work on.