I have heard of people playing with their wrist; flexing from their middle joint; pulling the string up like its a sticker. Well... I am here to tell you please do not do any of that. And here's why...
Playing from your wrist is a waste of energy, plus it is not precise. Flexing from your middle joint like you are scratching an itch puts strain on the tendons in the back of the hand, and it lacks power greatly decreasing the amount of sound production. Pulling up sounds awful, just do not do that.
Here is what you should do... play from your knuckles!
Exactly, it is supposed to be easy. Playing guitar is not supposed to be hard.
Here is a video showing how to play the fingerstyle and classical guitar with your fingers, and the movement starting with your knuckles.