If you are not a child you will find it helpful to do some stretching before each lesson. Stretches that emphasize the legs, inner and outer thighs, front of thighs, buttocks and back. Be sure to check with your doctor before beginning any new exercise regime. Your instructor should begin each lesson with some appropriate stretches but you will still benefit by doing some on your own before you mount up. When in class, be attentive and if you do not understand something ask that it be explained further.
Children spend many hours a day in school and are accustomed to being taught.
Adults have often forgotten how to be students. They have also forgotten how to make a mistake since they usually arrange things so they stay out of areas of doubt. Be prepared to flub-up and don't worry about it. It is all part of the process. Riding is a discipline so remember that while your instructor is explaining something she or he is not intending to give you an opportunity to sit sloppily out of position and let your mind wander.