"Start with the end goal in mind." Ok, so my end goal is I want you to buy my app .. so how do I work back from that to great copy ? The only thing I came up

"Start with the end goal in mind." Ok, so my end goal is I want you to buy my app .. so how do I work back from that to great copy ? The only thing I came up with is: "YOU GUY, BUY MY APP!" .. maybe I missed the point?