Definitely do not bring the top you care about. When I took my first lesson, it was a basic course that familiarized me enough with the machine that I would be allowed to rent time on it. They had a plain 1 yard piece of fabric that we loaded.
I think the key thing is take something you don't care if you ruin it. It is freeing and you won't be all tense worried about messing up on a top you care about.
I never did rent time at the shop because I realized immediately that LAing was the type of thing that took some practice and involves muscle memory. Two things I would never realize with sporadic rental time. So I bought an Innova. Here is a link to the very first quilt I did on it. I explained in this post how having a top I didn't care if I ruined allowed me try a lot of things most first time longarmers don't because they are afraid of messing up. When I did this quilt I only had the 1 class under my belt and had practiced on a one yard piece of fabric that we loaded when the LA was installed.
My first quilt off the longarm