I Wonder What Would Happen If...
You are about to sit down to practice your instrument. As usual, you have "should's" and "have-to's" swirling around your head. Take a second to focus on what is in front of you and try this out:
Before you pluck a string or make a note on your instrument. Complete the sentence, "I wonder what would happen if I..." Seriously, say it out loud.
Then play. Limit yourself to playing something extremely concise - one note, 2 seconds of music, music that is so contained that you can observe like a hawk without mental assessments kicking in.
Describe what you observed with adjectives other than good, bad, ok, etc.
This lesson from NEC faculty, Warren Senders, has helped me focus into my music countless times. As Warren would say when we would worry in our improvisation class that we would mess something up, "you can't fail if you ask yourself this question, because you will always learn the answer."