Make sure you keep yourself hydrated! Drink water, and plenty of it! It not only cools, you down but keeps you fresh.
Stay out of the sun if you can.
If you have a pool, use it! (Don't forget the sunscreen!)
If you want a nice icy treat, soak a bandanna in water, and pop it in the freezer. Then unroll it and place it around your neck. It will keep you cool.
Check your local news for cooling centers if you don't have air conditioning.
Bring your pets inside for them to stay cool! Pop some ice cubes in their water so they have a cool drink too!
A lot of these tips are common sense, but I thought I would share with you just as a reminder!