Eat a healthy snack about 30-45 minutes before you exercise to maintain your energy levels and get through the whole workout. Pick complex carbohydrates like a banana or toast with peanut butter.
Come to class dressed comfortably and make sure to wear long bike shorts or capri pants. If you wear shorts, your thighs might rub against each other when you are cycling and cause painful chafing.
Bring a small towel with you to class to wipe your face. You will sweat A LOT!
Bring a cold bottle of water with you to class. You will appreciate the refreshment after you're covered in sweat.
Pay attention to your instructor because they will give you instructions and the motivation you need to power through your workout. Don't hesitate to ask questions if you don't understand something.
During your workout you will get tired and may want to quit...instead you should feel motivated and push yourself until the end. You will be amazed with what you can accomplish if you just believe.