OK, here's one of the most essential (and weird and true) uses of making mistakes. Most awesome, amazingly fast players and singers get there by slobbing their notes and aiming for the downbeat and even just hitting the first beat of each measure. That is, in a 4 beat measure, they are playing 16, 24, and even 32 notes, but those 16, 24, and 32 notes are not perfectly in time; each note is not exactly 1/16th or 1/24th of the measure, rather some of the notes are early, late, too long or too short. But by concentrating on arriving at the downbeat of each pulse (and again, lots of times that's actually just the 1st beat of a measure and each of the other 2 or 3 beats weren't perfect) the unity of their awesome solo is provided. It's like an optical illusion, but it's an aural illusion - like the eye tries to make everything it sees logical and fit into a pattern, the ear does the same. In this amazing solo, scale, pattern, exercise, arpeggio the ear hears these slightly late or short notes, but because the soloist arrives consistent on 1, the ear says - yo, I'm cool wi' dat. And allowing themselves those 1/16th and 1/32nd note errors of time lets great musicians cross the bounds of their current abilities and achieve new heights of amazing, blazing speed. Try this in your practicing and soloing and check out some of your favorite shredding and otherwise superfast heros and see if you don't hear them doing that sometimes, probably even frequently.
No tension. Position your body so there is no tension in the neck, head, chest, or body. Chest high, shoulders back, dropped, and relaxed.