Relax. Absorb all the information that you can while you're in acting class. Watch other actors as they perform and take notes as the coach gives notes and gives the actors adjustments for their scenes. Keep in mind things from class that you can use when you practice with your scene partner.
Prepare alone first. Go through the scene that you are working on for class and break it down. Apply the techniques that you have learned in class. After you have done the emotional work, memorize your scene. This will help you in practices with your partner, when you have your lines memorized and you come in to rehearsal ready to work.
Practice, practice, practice. Get together with your scene partner as often as possible and run the scene. This will give you ample opportunity to try different things with the scene that you think might improve it, or different ways to play out the scene. It will also help you get comfortable with the scene and performing it.
After you've practiced, go back over your scene alone again and apply the work that you and your scene partner have done together. Focus on that work, apply it and prepare it again for the next time you rehearse.
When you put your scene up in class, remember that class is a place where you learn, where you become a better actor. So, be confident, be prepared, do your best, and adjust your scene as the acting coach tells you. Most importantly, relax. This is a class of your peers and in the end, you will all grow as actors together.