Is there a way to grow my hair longer?

Ok so ive always had short hair. My freaking haircut is always so goddamn regular. Number 2 and clean up the edges...sucks. Also because its so short i use body wash not shampoo to wash my hair. The end result is my hair has dandruff and i believe split ends. But ive tried growing it out before and it goes into a curly freaking weirdness. But this time i want to really grow it out. So is there steps to increase the fullness and make it healthier so it can grow faster...well not so much faster but rather consistent? Would it take longer because ive always had short hair? And can i trim it up while it grows to keep it presentable? And finally can i straighten it once its the desired length without it looking emo-ish...(nothing wrong with emo but not my cup of tea)? Any help would be great thanks!