You want to be somewhat balanced, you should still have weight on your front leg, but in general you're supposed to keep more weight on your back leg. Your front leg is direction, and your rear leg is the driving force. Shift your weight over to your front leg when you want to throw a right hand, shift it to your rear leg if you are throwing with your left. Make sure that you don't lead with your head, I mean don't reach with your punches and put your weight on your front leg. If you keep most of your weight on your front leg, it'll be harder to move, take away your punching power, and make you prone to a bad ko.