Look on the internet for a picture of someone playing your instrument.
Now play your instrument in front of a mirror or get someone to take your picture.📷
What differences can you see? If you play the violin is it on your shoulder (good) 👍 or under the front of your chin (not so good)🤢?
If you play the cello is it straight between your knees👍 ?
When you play your violin or cello, make sure that the bow is straight and parallel to the bridge. 👍
If you play the piano are your fingers slightly curled 👍 or flat 🤢? Flat fingers will make it hard to play quickly and the notes won’t sound so good.