Before actually going to your diving lessons, students should take the time to prepare themselves beforehand. We are not only pertaining to the physical requirements you have to meet. After all, you also have to be in the right mental state to start diving.
That being said, you need to do everything you can to not only maximize your physical capacity but also your self-confidence. You need to be comfortable in the water. Try to swim as often as you can to learn full underwater body control.