It all depends on the individual instructor and what the protocol of the lesson barn is. Your first lesson could include catching your horse in the paddock, grooming, and tacking up, or your horse may be all ready to go and you just have to mount up. Regardless, most beginners are excited and a little nervous so don't expect to learn much more than the very basics at your first lesson. I like to teach correct position and stopping and directing the horse at a walk on the first lesson and nothing more.
There are a lot of good books and videos that can be helpful and give you a better understanding of what your instructor is having you work on. I would be hesitant about getting too far ahead of your instruction with your homework though. A good instructor sees your strong and weak points and knows what you should be working on.