The basics of good form (ergonomics) and the study of movement (kinesiology) is a foundational building block of playing any instrument. If guitar is a tool to make music, let's look at the mechanics of correctly building speed, strength, and dexterity. Below is an overview of hand technique, body mechanics, and efficient conservation of motion and energy to play like you struck a deal with the devil.
Attention / Awareness
Pay attention. It sounds simple, but like a form of meditation it can take a lifetime to master. If you can focus your attention on something and notice all the details you're gold. "The devil is in the details."
“It's not about the number of hours you practice, it's about the number of hours your mind is present during the practice.” — Kobe Bryant
If you're self learning record yourself (video & sound) to check your form. Review and correct during the practice session.
The hand is one of the most complex movement machines ever made. Thousands of years of evolution have made it extraordinary good at fine motor skills, coordination, and flexibility. Repetition of an action creates physical changes in your nerves that help you to perform that action more accurately. This is called muscle memory.
*It can work for you or against you. It is extremely important that you practice the correct movement and not various combinations of correct/ incorrect or you will get inconsistent results.
Watch how a great player is producing a sound you like. Take inspiration from how efficient they are. This is a good move to learn a technique.
During all movements pay attention to your muscle tension in your fingers, hand, and forearm. Practice keeping muscles relaxed. Tension in muscles can be a hard thing to grasp at first. Some tips: stretch exercises targeting correct muscle groups, read about biomechanics, smoke weed (for the perspective shift & increased body awareness), and meditate.
Finger independence is important factor in efficiency of movement. It influences your strength, speed, and dexterity. It is built with a deliberate practice routine and practiced using the above principles of muscle memory. You can build this with anything you practice on guitar: finger exercises, techniques, riffs, licks, chord changes, strumming patterns, finger picking, etc.
[ex] Notice how if you set down your ring finger to play a note and it results in your pinky moving involuntarily. Isolate that movement and work on getting the pinky finger to relax to develop finger independence.
Placement & Movement Mechanics
Practice good form from top to bottom. Make it consistent. Seek out the details of the techniques. Pay attention to your efficiency of movement, relaxation, and synchronization.
[ex] Fret hand placement: correct finger tip placement, wrist angle, and thumb placement are critical to prevent future injury and get the best sound out of your guitar. It can change depending on what you're doing (i.e. playing scales vs. bending notes).
Economy of Motion
Take a logical look and apply the basic rules of physics to your advantage to play notes with force but at the same time the least amount of motion and effort. The goal is to make your guitar playing sound the way you want, while using the most efficient technique to achieve that goal.
[ex] If you're changing between two chords and you can keep a finger on the same fret or string, keep it down.
[ex] Fingers resting on the pick guard or the edge of your palm resting on the bridge. The anchor point.
Patience. This is not a skill that develops quickly. This isn't going to be a 4, 8, or 16 week thing. It may feel like you hit a plateau at some point; keep going. That practice compounds and will eventually pay off with a breakthrough. You will develop better feel, tone, and timing.