… from scratch, but with all your experience from playing the guitar for x years (decades ?), how would you approach it now ?
Maybe just this, although I don't have all that much experience in comparison to others on this forum:
Practice rhythm - Chord shapes, patterns, styles. Play along with a backing track and play rhythm. When you can play the “basics”, maybe then focus on ways to make rhythm more interesting, add some fills, use different chord shapes or locations, change your strumming. Listen and watch what more accomplished folks do.
Practice counting (licks) - Counting a lick is tedious as hell, but what I’ve learned recently is that although I can learn a lick without counting, I can’t figure out when to use it when I play along with a backing track. I’m either late/early and don’t play at the right tempo. BUT, when I count along with the track (not easy at first), the licks seem to fall in place where they belong/sound good. It's nice when improvising to have a lick that will work in a particular spot, but if you can't plug in the lick at the right time, you're going to lose your place.
Practice stringing licks into solos. In other words, take the licks you’ve learned by counting, and drop them into a solo for 12 bars. Mix up the order of the licks, skip a bar, listen to what you’re playing, record yourself, save the recordings and go back and listen to your progress.
Find a way to play out with others, somewhere. Go and make mistakes, give yourself a break, get comfortable with what you can do and what you can’t. Then give yourself a pat on the back for having the guts to play in front of others. It's pretty useful if you can have someone record it and go back and watch it later.
Don’t spend too much time/frustration on a particular skill and give up. Let it breath a bit. I’m still trying to get comfortable playing the Texas Shuffle (BGU 2.0, Lesson 10, part 2). It used to sound like crap, now it’s getting almost acceptable. I spend 5 minutes or so on it almost every day. It’s still not good enough for me, but better.
Lastly, decide on what’s “good enough”. That goes to the whole goals thing. What are your goals? Do you want to play just at home, in a jam, in a band, for fun or money?
My son is a classically trained musician, he works on things when he practices his clarinet that only dogs or other people at his level could hear. His goals relate to being a principal clarinetist in an good/great orchestra. He’s been playing and practicing in a wholly focused manner for the past 20 years (he’s 32), and only now does he feel like he’s getting somewhere. His goals are set pretty high, and they have become part of his life/identity. It’s the only thing he’s ever wanted to do and that hasn’t changed.
Me, I just want to keep trying to get better, and for me I know what that sounds like. I’d like to think that every day, no matter how well practice went, that I’m a little better than I was yesterday. That may be self-delusion, but it does help me keep going back to practice the next day.
I believe some focused practice every day is cumulative, and it will pay off.