Catching a clean correctly can be broken down into three elements that need to be addressed separately. They are: Mobility, the Finish and Meeting the Bar.
Part 1: MOBILITY & STABILITY
The first thing we want to address is the Front Rack position. Establishing an optimum front rack position is something we stress a great deal with our athletes. If you don't have sufficient mobility then stabilizing your shoulder joint and your Thoracic region to maintain a solid front rack is going to prove challenging. For more information and techniques to mobilize these areas, resources such as www.mobilitywod.com by Kelly Starrett are invaluable.
Establishing an externally rotated shoulder position is the first key. Using band assisted pre-torque strategies for developing mobility is a great starting point. Grasp an a anchored band with a supinated grip. The crux of the elbow should be pointing to the sky before you begin adding tension. A partner assisted stretch involves putting the athlete into a front rack position using a pair of squat stands. Keeping the hook grip in this drill is preferred but not required. The partner steps under the athletes rack position and applies pressure to triceps and elbows in an upward and outward. The focus for the athlete should be to drive up into the bar with the front deltoids while sitting the hips behind the shoulders. CAREFUL it's easy to pinch the Carotid Artery and cause the athlete to pass out. Communicate consistently with your stretchee, checking to make sure there is no light-headedness.
Part 2: THE FINISH
Once we have achieved the prerequisite mobility, the next area to focus on is the top pull or the finish.
Finishing the pull properly will help with the speed of your transition. The sequence of motor unit recruitment in the extension from the power position is critical for the athlete to understand and master. All force in the body starts proximally and moves distally. The hips must initiate the extension followed by the legs. Complete the hip extension by driving the hips up. This will create a reverse stretch in the hip flexor and put the athlete in an ideal position to pull under the bar. Simplifying the movements to focus on finishing the pull is a good strategy. Work from the high hang and off of blocks to ingrain proper sequence.
Part 3: MEETING THE BAR IN THE CATCH
One of the most beneficial aspects of the Olympic Lifts, and the clean in particular, is that it provides a tool to simultaneously train force production and force absorption. To that end, avoid the dreaded Pull and Pray or Pop and Drop strategies at all cost. You must maintain tension on the bar throughout the catch phase. The correct way to accomplish this by using the traps and lats to pull yourself down into position. Try and keep your hook grip through the entire movement if possible. If not, make sure and release the hook at the latest possible moment. Stay vertical in the catch by pulling yourself into the correct position. As you meet the bar with the shoulders, be prepared to absorb the force. Keep the core and adductors tight to catch a bounce out of the squat.
A great drill to teach the athlete how to pull themselves under the bar is called a Dead Hang Clean. Starting from a fully extended position the athlete must engage the correct motor units and ingrain how pull down in the proper direction. If you are having issues with upper back softening and rounding, specific assistance lifts (like Cal Strength Extensions) can be applied to help target and strengthen the Thoracic region.