I've been in your shoes. I've gone down the path of trying to learn things that just were not helpful or within grasp, so I'll throw a few alternative ones out there that were useful for me, but may or may not be for you.
A language is up there, so good on you for that.
But, first and foremost, organisational skills are a must. I found that by organising all of my documents, doing my washing before it pilled up, cleaning the house before it really needed it, getting into a routine, paying my bills, getting my drug dependency under control, etc. all to be very useful for my productivity. Another one is exercise - just getting out and going for a walk, or going for a run if you dare
Then there is mindfulness, which is an absolute must for those getting over dependencies of one form or another. Just sitting out in the sun is a good place to start.
As for skills, I learned to touch type. That was a good one. Another one that helped was to configure, clean, and order my computers and operating systems, so that everything is neat - scanning imoportant documents so I could file away the hard copies, for example.
You can never underestimate efficiency and effectiveness when self-efficacy is your goal, which it should be for all
