For a musician to accept a new knowledge, they must first attain physical, emotional, mental and musical, comfort and abilities. With these abilities, they may envision a goal and then create a path towards achieving their goal.
The first step towards a successful practice or performance is to prepare oneself with the necessary skills. The physical skills necessary include relaxed hand positions, correct placement of the hands and posture, as well as the dexterity to move along the instrument and produce the desired tones. The emotional needs are just as vital. The musician must feel at ease with themselves and the others in the room, such as their teacher or audience. As a teacher, it is vital that the student not feel criticized. The mental abilities include comprehension of the skills necessary for the piece as well as the ability to concentrate. The musical skills needed involve both the ability to envision a desired musical concept and to hear its enactment.
The next necessary ingredient is to envision a goal. Hear in your mind a note, a tone, a phrase in the most beautiful expression imaginable. Sing the note, solfege the note, walk the note, picture a color for the note, conduct the note, imagine playing the note. Once you have rehearsed this note in a variety of ways, play the note and enjoy it!
All too often, musicians, particularly advanced students, have a consistent negative dialogue running in the background of their thought process while they practice and perform. "No! Wrong! Out of tune! Missed that shift! How could you forget what you just learned!" Many musicians accept this as a necessary evil of self critical performance and the ability to improve. This is not only unnecessary but actually harmful towards the emotional, physical and musical well-being of the musician.
Playing an instrument requires a great deal of physical, mental and emotional energy. Wasting it on self deprecation is particularly useless. So how, you may ask, does one notice the errors so that they may improve their performance? They recognize them as information and not mistakes. For instance, if your finger landed in the wrong place on a shift, make the mental assessment, "that was too high" then try a positive alternative-landing lower.
If consciously setting a positive alternative does not at first work, break down the passage in a variety of ways. Find ways to make the passage simpler. Try walking, singing, playing it on an open string, playing in a different dynamic, without vibrato, in a different octave, with only the left hand fingers, the list goes on. Bit by bit, add to the passage until the original version is accessible.
Once the passage has been rehearsed so that all the technicality has been attained, play from your heart! Always singing in your mind the music as you envision it and then allowing your mind and body to follow your imagination.