The Law of Polarity states that everything in the physical universe has an opposite - such as Negative-Positive, Up-Down, Hot-Cold, etc.
One of my favorite discovery (practice) techniques is to use this Law to rethink how I play and listen.
here are some examples -
1. listen to the notes / listen to the silences
2. listen to the attack of each note / listen to the sustain of each note
3. feel the fingers press onto the fretboard / feel the fingers lift off of the fretboard
4. feel the fingers pluck the strings / feel the fingers release
Most of the time, we tend to think and listen in habitual ways. By using the Law of Polarity, we can develop more awareness - which leads to better playing.
For example, we can be so concentrated on plucking the strings that we don't think about the release before and after the pluck. This is one of the reasons why we have unwanted tension. Focus on releasing.
With the left hand, we may think only about the act of pressing onto the fretboard. The fingers do not lift fully, because we are more concerned with the next press. Again, this creates unwanted tension and fatigue. Focus on lifting.
In listening, the attack is the most obvious part of the note, but even more important is the "body" of the note. Hear and feel the rest of the note - listen carefully to the decay.
We sometimes think of silence as a gap between the (more important) notes. Silence is where all sound is born and dies. The more meaning you give to silence, the more meaning your notes will have. We want to cultivate a deep reverence for it.