Jabbing Mistakes.

[Andre]

Lifting the elbow.

Leaning forward. Letting the weight ride up on the front foot. Pushing off the front foot.
When you step with the jab...the front foot hitting the floor before the fist hits the target. Not moving both feet.
Not turning your shoulder into the punch. Not turning the punch over. Short arming the punch, not driving the arm all the way out.

go to a pub and play a simple game of darts.

Yeah but dart players dont have to worry about openings on over commitment or recovery to balance or need to counter anything, some keep their arm out after the movement too and the rear leg balances them.Just wondering if you are talking about aim concerning them if not then what part; full extension?

Understand the elasticity of a rubber band and its retraction

Understand Im a mod and can see all five of your other user names and prior history which adds up to exact reason you choose answer this way.
Your future is in your hands here.