My favorite hand stretch comes from my Tae Kwon Do training..
Extend an arm out straight in front of you.
Reach out with the other arm and pull back on your four fingers to feel your carpal tunnel tendons stretch out. Be gentle and kind to yourself.
I have small hands. I have found that simply practicing and learning how my finger positions feel in order to play a clear open chord is very helpful.
So, yes. Like the old joke goes . . .
A pedestrian in New York City stops a cab driver and asks "How do I get to Carnegie Hall?"
To which the cab driver replies "Practice, man. Practice."
I hope this helps.
Peace, Love and Understanding
/David C.