Stretching Exercises for Piano Players
Pianist's technical problems are almost always related to tension and stiffness in the shoulders, arms and wrists. To overcome these problems, the player must re-learn patterns of coordination so that the shoulders and arms are involved in the playing of each note. There must be a coordination of movement so that energy flows from the torso through to the fingers on the keybed without be blocked anywhere along the way.
Before starting in playing the piano, I have found that it is invaluable to go through a stretching routine to warm up the arms and release built up tension in the body.
The routine I have developed involves three stages: Releasing Tension, Warming Up the Arms and Shoulders, and Warming Up the Hands.
Releasing Tension
Start by standing and stretching all over, whatever feels good. Take some deep breaths, voice HA on the exhales, feel free!
Bend over from the waist, stretching the arms down to the floor. Let the arms hang, then slowly roll up from the waist. Let the arms hang down, then let them roll up from the shoulders.
When standing, shake out the arms from the shoulders. Feel the entire arm as one connected structure.
Bend at the knees, then let the arms drop. Lightly bounce on the knees, letting the arms bounce, with the shoulders very free.
Warming Up the Arms and Shoulders
Standing, move the arms in large rotations, 5 in each direction. Do either one arm at a time or both arms together.
Do large Figure 8 motions with each arm, 5 in each direction.
Shake out between each segment!
Sitting at the piano, bend over from the waist. Let the shoulders roll over and lead the arms down to reach for the floor. Lift the arm up - from the shoulder - and let the shoulder lead the arm and hand onto the piano keyboard. Do this several times, making sure that the fingers are not reaching for the keys.
Make sure that these large motions are starting from the shoulder, there should be no reaching with the hands. Let the arm and hand follow the motion from the shoulder.
Warming Up the Hands
After stretching out the arms and shoulders, the hands and fingers need to be warmed up.
Repeat the shoulder roll up while sitting, but this time let one of your fingers come down onto a key - any key, and concentrate on moving from the shoulder. There should be no reaching for the note with the finger. Feel the weight of the arm sinking into the piano keybed, then slowly move the entire arm left and right with the key held down:

Do this with each finger, letting the finger slide on the key.
Let one hand drop onto the keyboard, play a diminished chord or just a random cluster. Take the other hand and rub the hand and fingers into the keys:

Let both arms drop the hands onto the keyboard, and with flat fingers, sweep the fingers up and down the keyboard along the black keys. Do this for several minutes, feeling the motion starting in the torso - this is a big arm motion that wakes up the fingers:

Stand up, shake out all over, and roll the shoulders again.
Take each finger, and massage it with the other hand. There are many different ways to do this, the goal is to wake up the muscles on the sides of each finger.
Here are a few ways to wake up the fingers:

These stretches are very helpful if they are done before and during every practice session. After playing for a while, stand up and shake out your arms, do some shoulder rotations, and run your fingers along the black keys.
These stretches will help you learn new coordinations making your playing stronger!