Jerk Rack: Relax Your Grip
If you tend to push your jerks forward, or let the bar slide down in the dip, check your grip in the rack.
When your grip is too tight, it will tend to pull the shoulders back, meaning the bar can move as you dip and drive.
It will also tend to make you push both early and forward with the arms.
When you get ready to jerk, try consciously relaxing your grip and feeling the bar settle securely in the rack.
Remember that the key with the jerk rack is to connect the bar directly and securely to the trunk so the force of the leg drive is transmitted completely.
Anything that disrupts that connection, such as the bar moving as you change directions in the dip, means force loss—just like your tires spinning when you accelerate in a car.
Early pushing with the arms also means less leg drive force, which means less speed and elevation, which means less opportunity to get yourself under the bar properly.