1) Be sure your dog is getting a complete and balanced diet. A good diet goes a long way in helping your dog keep up his energy. To prevent an upset stomach, don't subject your dog to strenuous exercise directly after eating a full meal. Save mealtime for after the hike when your dog is rested and cooled down.
2) Avoid heat and humidity. On those hot and/or humid days, hike in the early morning or in the evening when it cools off. Dogs with dark or heavy coats tend to overheat quickly.
3) Be sure there's plenty of water. Here's how to calculate: Your dog needs 12 ounces of water before the hike, 12 ounces every half hour during the hike and the same amount afterward. An alternative is to hike by a stream.
4) Watch your dog's paws. Hiking in the woods can cause footpad injuries such as cuts and scrapes. Remember to bring along a first aid kit and attend to any problems immediately. Keep your dog's nails trimmed so they don't get caught in grass, which could cause serious injury.
5) Leash your dog. It's really the only way to maintain control at all times. This is especially important in the woods where you want to keep your dog away from other animals and dangerous plants like poison ivy.