All excellent suggestions above. Another thing I do is to be sure I don't spend much time outside in the sun the day before a ride, be sure to get the yard work, mowing, whatever done a couple days before the ride. Staying inside out of the sun/heat and soaking up the AC, (and water) the day before, (or even a couple days before), makes a big difference as to how well you handle the heat, especially as you grow older.
Ride safe,