You should set yourself a realistic goal for your indoor cycling workout. Whether it is to burn a certain number of calories, work on a specific skill or just having fun.
During your first class it is important to familiarize with the resistance and pacing. Get used to the resistance levels, take it easy first, and gradually increase intensity.
Watch your body form. Keep your back straight, engage your core and maintain a steady pace. This will help you avoid injuries and get the most out of your workout.