It is very difficult to simply "stop" poor technique. When, despite our best efforts, we realize that we are still engaged in a negative habit, Practice Monster has a temper tantrum. A far more effective method is to replace a bad habit with a good one. I use this technique in my own practice, and in my teaching. Here's an example of how it works.
Problem: As the student plays into the high register of the saxophone, she stretches her body upward. Even her eyebrows ascend, and the resulting tension makes the sound pinched and unpleasant.
Solution: Begin by practicing ascending scales. As the student ascends, she bends her knees and slightly squats downward. She moves the eyebrows downward, relaxes the forehead, and focusses on doing exactly the opposite of what she did before.
In time, the student shifts towards thinking about the exaggerated opposite, without actually doing it. After extensive practice, the student might be able to accomplish the desired result just by slightly bending the knees, or softening the muscles around the eyes.
This technique works because not doing something is abstract, but focussing attention on the exaggerated opposite gives a tangible target. The undesirable habit is methodically replaced with a desirable one.