It sounds cringe, but playing in front of a mirror (once you don't need to constantly look at the fretboard) is one of the best ways to spot poor technique.
Look up some "guitar heroes" (Brandon Ellis, Samy Elbanna, Teemu Mantysaari, Jack Gardiner, Guthrie Govan are a few examples) and just observe what their posture and hand positioning looks like and then play in front of the mirror to compare. If your posture/technique looks significantly different that means you have room to improve!
This was one of the biggest catalysts for skill gains in my novice years.