Don't wash your hair too often. Don't use a hair dryer. Don't use a flat iron. Don't use hair ties. It seems like everything you do damages your hair. For me, I can skip the hair dryer most of the time, but I can't skip my flat iron. I also dye my hair and have highlights, so it does show signs of damage.
You can't repair damaged hair, but you can use products to make your hair look better. Here are my best hair products for damaged hair, and I'll give you some great DIY recipes too!