I started out by teaching myself BASIC on a Vic 20, and in college (mid 80's) I had Fortran, Pascal, limited C, machine and assembler (With a smattering of COBOL) as part of a computer science minor in college. I didn't touch programming from approx 1989 to 1999.
At that point, I was lucky enough to get hired as a Clipper programmer. Took me about 6 months to learn most of it, and by now (13 yrs) I'm pretty expert in it. I have also picked up Cold Fusion, some C#, some ASP, SQL, etc. I know programming structures, but in most modern languages I'm missing the esoterics, and I know my code could be much tighter.
The problem is that I've learned what I needed to, to get the job done. This results in a lot of gaps in practical knowledge. I am also missing out on a TON of theory. Things like SRP, Refactoring, etc are alien terms. (Although I grok the intent after a short read).
In addition, I am in the position now of teaching junior programmers the company and our software, and I don't want to pass on the knowledge gaps. I know this is somewhat of a subjective question and may be closed, but how do you go back and pick up what you've missed?