I put together an exercise to work on this, which has done the trick for me. Work on each group separately, lightly and quickly as possible, and preparing each motion at the earliest opportunity. Feel each repetition as a single impulse, and allow yourself to relax completely after each rep before repeating. Don't worry about working with a metronome, just see how fast you can do it. When it feels natural, try some scales and try to maintain the same mental and physical state.
This is a different way of working than I presented in my recent post about developing the right hand. I am having dramatically faster results with this new way of working, but I can't say for sure whether it should replace the other way or be used in tandem.