Shortly after writing about Maya Moore and the tendency of her right knee to cave in when decelerating, especially when she stops to shoot as evidenced in the video, I worked with a young player with similar issues.
To address the improper muscle firing and gluteus weakness, I introduced a couple exercises to activate the glutes.
A more advanced progression from the Clamshell is to use a wall and a straight leg:
I did not address any hip tightness with this player, but if tightness is an issue, here are a couple exercises:
IT Band Foam Roll
IT Band Stretch