HOW DOES YOUR BODY FEEL?
When I learned how to drive a car it was really funny and painful to watch me. Panic in eyes and supertensed body. I sat with extremely straight back and hold the wheel so vigorous that my fingers hurt couple of days after the driving lesson. In my attempts to control everything and do it «right» I doubted I could ever enjoy the process and drive a car without such a stress.

Working as a jury member on piano competitions I see sometimes participants who remind me about that experience.
Non verbal self-presentation - gestures, walk, posture - give us more information than just playing itself.
Quite rare you'll find a free sound in a tensed body. Quite rare you'll find a free voice or natural interpretation in a tensed «blocked» body.
That's why a very first thing I recommend my students is to notice HOW your body feels during your play.
1
Do you breathe when you play? How do you breathe?
2
What happens with your breathing right before you start to perform?
3
Where do you have tension when difficult spots are coming?
4
Where in body do you feel tensed / uncomfortable when you think about an important performance?
Being concentrated is not the same as being tensed!
If you remember your coolest performances you'd probably notice it was a good combination of freedom in body and focus in mind.

To be more aware of your breathing and body is one of the most effective way to improve your play.
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