As much as you can, drinking plenty of water leading up to your desired class time. Not forcing it and drinking too much causing you to want to have to urinate frequently as a result, but by having being mindful and having water near by you throughout the day and sipping on it as you feel the need. If you are taking an earlier class in the day, just doing the same by drinking what you can before the class time in order to fuel the body, as best possible, with water.

The same goes for after class, as you really want to then re-hydrate after sweating so much during the class. Basically treat yourself well after class by having lots of water, and refueling the body by also eating well. This will only help to heighten all the hard work you are putting in during the classes.