After years of "practicing" (really I was just fucking around playing licks, riffs, and strum patterns with no direction) the #1 factor in my development as a guitar player was the concept of deliberate practice. It is fundamentally about three things: focus, feedback, and consistently pushing yourself to the edge of your ability.
Understand the do-or-die importance of focus. If you can't focus when you sit down to play you risk the slippery slope of distraction, judgement, and self-doubt fucking you up. Notice when your attention has wandered and bring it back over and over and over again. This is the basis of meditation.
Pay attention. Really listen to the notes, the mechanics, the movement, hand & finger position, and your body posture.
Define specific, measurable, actionable, relevant, and time-bound goals. Example: Play a song all the way through, at 85 bpm, with no mistakes, three times in a row. A structured practice routine with steps on how to execute is key.
Practice everyday. At the start, it can be 5 minutes. Work your way up to 15, 25, 50 minutes of focused practice. No autopilot rides. Try out time variations of the Pomodoro technique.
Be deliberate. Focus on building and improving specific skills by breaking them down from the bottom up. Deconstruct them from the fundamentals. Start with the kinetic motions.
If you fuck something up when playing, don’t power through it. Stop, replay that part, slow it down, reflect on what went wrong, and correct it. Isolate that part and work on improving it. Only once fixed (in isolation) can you go back and put it context. This is fundamental to how you improve and don’t repeat mistakes.
Repetition inside the comfort zone does not equal deliberate practice. Deliberate practice requires that you’re at the edge of your ability and repeating it with feedback (easy for us musicians, listen [record it to review] and ask “does it sound good?”)
After each session, reflect on what you've discovered. What worked? What didn’t? Where do you need to improve? Where's your weak points? The idea is to get a clear sense of how a particular session impacted your skills, help set goals for improvement, and identify skill level plateaus.
As you progress with any skill you'll reach a plateau. Get creative and experiment with different methods and practice techniques (come up with your own, research the context for ideas, or consult a teacher) to break past your skill level plateau. Strive to always improve.
I can offer once piece of universal advice: "slow is smooth and smooth is fast."
"The point, therefore, of these arts is the doing of them rather than the accomplishments. But, more than this, the real joy of them lies in what turns up unintentionally in the course of practice, just as the joy of travel is not nearly so much in getting where one wants to go as in the unsought surprises which occur on the journey." – Alan Watts
Fall in love with the process and the discipline of consistent deliberate practice. Put in the work and show up everyday. There are no shortcuts to true skill development. Repetition and practice. It’s worth it, seeing yourself progress and nailing that part, then doing it all over again on the next thing. I recommend reading my guides on how to create a practice habit and how to setup your practice routine. It's everything you need to know to learn how to practice playing guitar.