Avoid heat exhaustion. Your choice of clothing should include wicking fabrics and layers, a hat, and sunglasses. Snacks should be in your day pack and you should monitor yourself for the symptoms of heat exhaustion. They include dizziness, fast breathing, nausea, increased pulse and clammy skin. Have an extra gallon of water stored in your car for after the hike.
Blisters are a bummer.
Notice any sensations that alert you to heat in your boots - and stop the abrasion immediately. Your day pack should have supplies to help you protect any of these spots and solve the problem. What you want to avoid is excessive trauma to the knee as well as the invitation to shin splints. Often experienced by hikers, shin splints are the inflammation of the muscle and fascia on either side of the shin bone. As in many areas of life, success favors the prepared person.