I am 19 years old girl and i tried many things to get longer hair but my hair still very short. please tell me what should i do for it?

Nothing: If you do not have bald spots, there is realling nothing to do. We usually would test your thyroid and look for other evidence of underlying health issues. The length that hair will grow is mostly genetic (there are long hair dogs and short hair dogs). How tall you are is also genetic. It is what it is.

Healthy hair: Get adequate sleep,avoid excess sugar & fat, v carbonated drinks, eat enough protein, exercise regularly. Insure you have adequate Iron (like kale & other dark green leafies), Omega 3 fatty acids (like walnuts),vit.E (fruits & veggies), D & B vitamins, biotin & zinc. Avoid sulfates & formaldehyde in shampoos, excessive blow dry heat & curling irons.