a good prestrafe?

Hi! im new at lj and i have watch the guide on this site alot but im wondering about how a good prestrafe should be done.

i know that u have to hold W D or W A and then release W at the end of the edge den start u first strafe but when i do this i dont jump longer so for me the "prestrafe" not help me to get a bettter lj.

so can some one explain me how a good prestrafe should be done and mabie look if someone can show me an example?

Type /speed , and gain as much speed as possible before takeoff.