Feeling like you are flying on a board it’s awesome! The instructors will help you set up the board, and then they will tell you what to do in order to stand up. Honestly, the explanation was completely useless for me. Once you get in the water and the watercraft gives you the power, your body will adapt to the impulse. At first is very hard to get up. You will probably stand up for 4 seconds, and that will feel like an accomplishment. After 10 minutes, your body will completely understand how it works. This is when you are going to have fun, you will be able to reach a higher height and remain in the air for multiple minutes.
In my opinion, you should book the one-hour class. Half an hour is too little, and two hours is too long. After 45 minutes you will feel VERY tired and sore. You will probably use muscles you didn’t know they exist!
If you own a GoPro camera you should definitely bring it. At first it’s going to be hard to shoot videos or takes pictures, but once you get use to the Flyboard you can start using the camera. Finally, don’t forget to bring water and/or Gatorade, sunblock and a comfortable swimsuit.