Becky and I joke weekly about how terrible her jerk is.  When we were at the training camp in Seattle her “twinkle-joes jerk” was one of the running jokes.  Here is a example of one of those jerks:
Becky Clark Jerk Analyis
My favorite fix for this problem is problem is the jerk squat or also called the dip squat.  These can be done from the rack or jerk blocks but my favorite is to add them in on clean workouts.  If you are completing a workout strictly of cleans with no jerk then it’s a no brainer to add these in.  If you struggle sending the bar forward when you jerk then give this exercise a shot.
There is no way you can successfully reach your jerk potential if the bar does not move in a perfectly vertical line.  If the bar moves even slightly away from you then you have to move slightly with it.  Any extra, unnecessary movement makes the lift harder.  In a perfect jerk the bar moves straight up from the shoulders and the lifter steps into the lift.  If the bar is moving away from the lifter then the step into the weight becomes harder and more exaggerated.  A perfectly vertical bar path is key for good jerk.
Check this video out of D’angelo Osorio and Donovan Ford doing cleans.  D’angelo is adding in the jerk squats.  The abruptness with which he stops on the dip is exactly how this lift should be performed.
Cleans with Donovan