3's and 5's are thrown very similar, 7's and up are different. My best advice is to first watch some clips of a cork 3, 5, and 7 and try to analyze it. Break that shit down from where the person throws the trick, which hand they lead with, where their eyes are looking, how they come around, etc. Once you've got that done, try visualizing yourself/how you'd go about it if you were going into a jump. Then read some threads on ns and figure out which advice is correct/incorrect and which of the correct advice makes the most sense to you. Visualize some more, try some on tramps if you have a chance (except for 3's), and once you feel comfortable with it-giver