How can I best prepare for my first lesson on stalls?
You will impress your instructor most by being eager to learn and learning quickly, and by having done book work beforehand.  Just do some reading on stalls and really get to know the 2002's Operating Manual, especially the numbers and limitations.

Be careful about trying to show that you already know it all.  If a student has taken the time to learn the operating manual and knows all the important numbers and limitations by heart, and can recite emergency drills etc while under stress, the instructor will way more impressed than if a student tries to show they already know how to do the lesson.  That being said, just read up, and really learn the manual.