Stay hydrated. I generally drink plain water on shorter rides. However, when I’m riding a century I switch to a sports drink like Gatorade with added electrolytes.
As a rule of thumb, I try to drink a water bottle every hour. To help ensure I meet this goal I set an alarm on my bicycle computer to sound at the completion of every mile. The alarm reminds me to take a sip of my sports drink. This technique keeps me drinking and makes my intake of water just the right portion that my body can process easily.