The other things you said are absolutely great too, regarding eating and habits, but I don't include those for me because I figured that out very quickly. I did not, however, figure out how to lift early on. And I didn't train legs at all to start. I also overvalued programming early on.
There are 2 lessons I've learned in the past few years that I value quite a bit. One is the value of training directly for competitions. It's a great way to force yourself through plateaus, and it helps tremendously with motivation when that's something that's lacking. If I have weights I have to hit in competition, and a bodyweight I need to make that, I'm going to give my training and diet more specific attention than I would have otherwise.
The other lesson has been that training with things other than barbells and dumbbells is not to be underrated. Building my base of strength through basic barbell training was important, and it's still what counts for 75% of my work. But handling strongman equipment opens up an entire world of strength that I wasn't previously familiar with. It's humbling, and really exposed my weaknesses. I would say that I should have introduced carries into my programing a long time ago. It makes sense to include them regularly after your first year or 2 of training, if not sooner.