I'm in little of the same boat. My first mountain bike will be here in a couple days. I've been a little nervous about how I will do. I'm sure I'll be fine and I'm sure that some of my bmx skills from my teens will instinctively kick in.That said, I'm older (by a lot), I'm heavier (by a lot) and the bike dynamics aren't the same. I went look for some tips in technique.
I found this video:
I don't know who he is, but he's really good at breaking down the basics in a variety of situations.