"Freedom in the ball and socket joint is important in violin playing. Angle your shoulder rest on the back of the violin so that this side sits on the collarbone away from the ball and socket."
It's important to regularly monitor your violin hold including the placement and height of shoulder rest. Ask your teacher to do this by walking round you and observing from all angles.
Video your playing from the left side to check your set-up.
This is especially important if you are a young student who is growing and changing shape.
For teachers;
Teachers should check the shoulder rest is still being put on correctly, sometimes there's a gradual movement away from the best placement. Watching the student from their left-hand side in a lesson is useful to check on their left shoulder. You could also video students from their left-hand side in practice and in the lesson.
Violin repairers and dealers do not necessarily understand how to set up a student's violin hold so it is important that teachers monitor what type of shoulder rest their students buy....