When should you start lounging over a jump?

[Got your Yee Haw]

Should you start lounging over jumps immediately in a routine of training a hunter/jumper, or should you complete his green horse training first, and then incorporate it in?
Please explain why you feel the way you do.
Thanks for the advice. What should a horse know before jumping begins? i.e. counter canter, lead changes, shoulders fore, etc..