I started 2 months ago after a 10-year hiatus, and it wasn't so bad. I remembered SO much once I was back on.
-- You're probably going to be sore, especially after the first lesson, so you may want to pick up some tylenol/ibuprofen and some sticky/disposable heating pads.
-- I completely agree with tinyliny about stretching, doing some walking, etc. Also, much like you, my biggest fear was that I'd look like an idiot after such a long break. But nope, trainer thought I looked good (all things considered) and once my muscle memory kicked back in, it's been pretty smooth. I'll even go back to jumping in another month or so.