I have been dabbling in guitar for over 20 years. I have decent dexterity, technique, and musical theory. However, I don't count time and never use a metronome. I always sound like a weak version of the spotlight guitar solo at a concert, doling out licks, scalar runs, and 'neat noises'. I know very few songs, and am a weird hybrid of "expert level" and "novice".
In all honesty, I live in abject fear of playing with others, because of my idiosyncratic sense of time.
The good news is that I am musical: I am an intermediate on piano, having learned "the right way", using the metronome, and I love it.
Clearly, for guitar, I need to start working with a metronome, but what are some effective techniques to overcome decades of bad habits?
e.g. Do I play scales, counting triplets and 16th notes? Should I just jam to backing tracks on YouTube? Perhaps just pick a single song and truly learn it all the way through? I realize all of these are plausible suggestions but I am looking for proven tips from those who have been through this journey.