The number of ways the human body can move is close to infinite.
This is why violin teachers often suggest sitting or standing still. Not to be mean, but to simplify the problem of being a human a little bit.
The easiest way to confuse yourself while practicing is allow for too many variables.
If you’re practicing a passage and it’s not working, you’re naturally going to make changes to what you’re doing until it works.
If you make more than one change at once, though, you won’t know which change has made a real difference.
This can lead to hours of unproductive insanity.
So get your posture in a comfortable position and keep it there for a while.
Play the passage.
Think about what you did.
Decide one thing you’re going to change physically the next time you play the passage.
Play it again using the change you’ve made.
Decide if the change you made was a good change.
If it wasn’t a good change, decide on a new change and try again.
If it was a good change you’d like to keep, practice the passage again enough times with the change you made in order to commit it to memory. This is important. Don’t introduce a new change until you’ve committed the old one to memory.