Horseback Riding Help?

I'm going to go to this horseback riding place in Skokie (my friend didn't know what the name was -.- ), and we're only going to buy a horse and equipment (including helmet, padding and all that), but no instructor. We're gonna be taught by my friends mom, who raised horses and rode them, both wild and tamed. I feel kind of nervous at this, even though she seems experienced. So, are there any basic tips I should know about horseback riding before I go? Like, what to do and not do in front of the horse, and how to stay safe when I'm with it, and all the essentials that I should know. Thank you!