There is still a topic on the board about setting up the left hook. I think many people assume that you just throw the jab and it lands or not. I don't believe that to be the case. Like any punch it always has a purpose. Lets talk about what you use your jab for- why you throw it in the first place. It sets up all the other punches, right? Well, how and why? So what do you do to really land that hard jab? How do you use it to set up other punches or to avoid the other guy's punches?
My friend used to spar with Emile Griffith and here is something he related to me that Griffith use to do often and successfully.
He would begin with feinted jabs to the body, his eyes noncommittal, then escalate to jabs to the body, his eyes sometimes up, sometimes down. One of two things would happen. If the eyes down fooled you into throwing a right hand at his head, Griffith would pull back from it and counter your short-of-the-mark right hand with his own right. If the eyes on your eyes froze you then he would bring his left straight up- a stright left upper jab, if you will- to the face. React or don't react, he had you set up because he was calling the shots and pulling the strings.