If you trim it about every 1 to 3 months it helps it grow faster because you won't have any damaged hair at the bottom or split ends. Also don't use alot of product or heat because it will just damage your hair and make it worst. Products with a natural base tend to work better and leave your hair in great condition. :)
Drink plenty of water, hydration is key. You may want to try a coconut oil hair mask, or deep condition your hair every once in awhile. Also get it trimmed regularly, and for shampoo I find suave to be the best/cheapest!