Hey man,
In highschool, I used to put on deoderant the night before and then in the morning. It helped prevent sweating in the armpit region to avoid smells. Plus I think there are shirts designed for that. They're padded in the armpit region to absorb the sweat. And walking in the sun with an umbrella helps a bit as well.
But going out in the evening or once it's cooled down helps a lot. There are times in the day when the sun's the hottest, so I'd stay indoors during those intervals. You can also socialize in buildings such as libraries, the store, etc.