One of the most common seen hideous problems of many players is that they are not bending at the legs and instead bending at the waist. This puts them off balance and creates undesirable shoulder rotation (and drop shoulder) that makes it tougher to control their shots.

How do you get rid of this problem through training and practice? You can ask someone to feed you low balls and hit them with your head still, point up. By the way, this pracice, besides get you to bend your knees, will train your athletic foundation and balance as well.  And, you can find more valuable tips and instructions in my book .