Everyone's hair routine is completely different, especially for summer, but if there is anything I can share it's called CONDITIONING.
Deep conditioning, especially in the summer, is the best thing you can do because your hair is naturally going to dry out due to the sun. By increasing the moisture in your hair, you can prevent breakage, overdrying, and even split ends.
Another tip, STOP shampooing! Not permanently of course, but try to limit your shampooing to twice a week. Instead of shampooing, try conditioning only. Your hair will feel like a million bucks, I swear.