It's largely going to be genetic. There are outlying issues, like if you have scoliosis or spina bifida which can cost you some inches, but otherwise it's going to be your genetics. One thing you can do to make sure you're growing is to make sure you're eating a healthy diet and getting plenty of exercise. Stimulate your muscles and your bones without damaging them. And get plenty of sleep at night.

I've also heard you get get a little bit extra with gravity boots or an inversion table, but I'm a little dubious on those claims.