I use to live in desert regions of California (Bakersfield & Mojave desert area). You obviously need to hydrate while riding, but not with just plain water; because when you sweat your loosing electrolytes, so you need to drink Gatorade diluted 50%. You should be drinking about 1 24oz bottle per hour. Also it helps to pre-hydrated the day before with about 48oz's of extra fluid; and then about 1 hour before riding drink 24oz's; then pee just before riding. One of the ways you can tell if your not getting enough potassium is muscle cramps; if you start getting those and your drinking enough you may need to take a potassium supplement before riding (Stim-O-Stam is what I use).

Also there is a pro and con to using sunscreen; the pro is that the sun won't burn your skin as fast thus protecting you from skin cancer; the con is that it makes your skin hotter because the sunscreen won't allow your skin to breath as well. I think the pro outweighs the con!

I usually tried to ride in the evening hours to get the cooler sunless hours, problem with evening riding there's more pollution, and morning there's more pollen!

I found that loose fitting jerseys worked better than form fitting because the loose jersey allowed the air to bellow into the jersey. Also wear a white jersey, it's a cooler color. By the way, Walmart sells white polyester jerseys (loose and form but no rear pocket) called DriStar between $9 to $12 and it works just as good as my expensive ones!