The following two technical problems are the first ones I find most common in students’ playing:
Number One: WRIST
The first symptom of tiredness or pain in the hand results from a Locked Wrist. This is a very common problem especially found in beginners (young and adult), and even in advanced students who did not develop a proper and solid technical foundation during their early training.
When students start playing, it is easy to just raise the fingers and press the keys down. That only initiates the fingers and simply separates them from the other parts of the hand and arm, making the fingers isolated from the whole working mechanism. Therefore instead, think more about playing with the wrist by moving it down (to press the keys) and up (to release the tension afterwards), in the execution of the same note at first (and of the long held notes in the long run), and then groupings of two notes and a whole phrase when such is done properly and naturally.
Number Two: ELBOW
A Locked Elbow tightens up your whole arm (forearm and upper arm) and limits its movement. When the elbow is pointing inward, it indicates that it is too close to the upper body.
In general, turn both elbows slightly pointing outward and keep the upper arms some distance from your torso. Let the fresh air through under the armpits, keep them cool and let them breathe.