Jungle Tips

Hey all, I've seen nb3 and people in videos get a high level lead over their opposing jungler. And I have no idea how they do it. I know it's from farming obviously, but I don't have a clue how they farm so much while being able to gank often, while I try farming a lot, but the enemy jungler get like, a two level advantage while ganking all the time even though he doesn't get anything out of it, and he has lower farm than me! Please help. All tips are appreciated. Tl;dr - how do you get a level advantage over enemy junglers.