How do I get long hair?

You wait for it to grow out. Take good care of it while you are growing. Lots of scalp massaging, good shampoo, healthy diet, & reduce the amount of heat and chemical damage.

Oh and frequent trims to keep the ends healthy.

You wait for it to grow out. Take good care of it while you are growing. Lots of scalp massaging, good shampoo, healthy diet, & reduce the amount of heat and chemical damage.

What do you mean by 'chemical damage'?

Dying, perming, or chemically straightening.