Take it easy while riding. Make sure you're in a good gear (not spinning around too quickly in a low gear, or having to really mash the pedals because you're in a high gear) and comfortable while riding. I assume you already have a water bottle cage--maybe put on a second if you can for extra hydration. Be sure to be hydrated already before you ride. Wear some comfortable clothes--you can find shirts that breathe, and have panels for air flow.