How many feet before the obstacle you take off depends on how much speed you have. More speed = more distance. Judging by the fact that you're just learning the movement itself, I can tell you that you don't want to be working with too much speed yet. Just a jogging pace. Don't worry about measuring distance, just jump at it when it naturally feels good.
And remember, your body is your own best teacher. The best way to learn is to go out, practice, do it tons of times and you'll progress much faster that way, than by watching any amount of tutorials or asking questions.
It's great to ask questions and gain some knowledge, but knowledge is the foundation and practice is the sustenance. You need both!
Practice lots, train hard, and good luck.
