Powering up your lunge

Proper Lunge:

Tips:

Train with light-moderate weight with speed, explosion, and accuracy as a focus. 

Train your retreat as part of your lunge training, don't casually reset your position.

Strength building exercises:

http://www.bodybuilding.com/exercises/detail/view/name/dumbbell-lunges 

http://www.bodybuilding.com/fun/brughelli1.htm