How do i make my hair grow longer?

My hair is touching my shoulder and i really want my hair to grow. My mom had always told me to get it trimmed every other month so i don't get split ends but it isn't growing that well. i got my hair short in a bob 2 years ago and getting it trimmed it's only made it to my shoulder. My hair does grow slow but not that slow. I haven't trimmed in 3 months and seen some growth to it. Is there any type of shampoo and special hair ingredient trick to make it grow faster. Also if this helps, i have very curly hair ( not so much frizz) but little ringlets of curls. I hope it grows super long! Thanks!