For your hair to grow longer you need it to be healthy so don't use straighteners and hair curlers as often. Your hair can also be effected by the sun so wear hair styles that keep most of it hidden like in a bun or braid. Don't brush your hair when its wet its weaker and breaks easily, conditioning your hair is also good for it and there are some shampoos that are made to make your hair grow faster. Don't wash your hair everyday it dries it out so your hair follicle releases more oil making it gross. Brush your hair often it cant grow if it has a bunch of tangles in it. Messaging your scalp raises the blood flow making it grow faster. Your hair grows half an inch each month most hair stylist recommend you trim it every 3 months but that will only maintain the length you have so change it to every six months (unless you get lots of split ends) so you can have an extra 4 inches a year. That's all i can think of.
Leave your hat on always works for me, have a hot shower and while your head is still warm rub some salt into your scalp the salt will keep the pores open which will stimulate growth. Do it every day for a week and see wot happen. Ps it worked for me.