It’s definitely a topic I’m interested in, though I can’t say I practice anything regularly. Eating some kind of baked fish (not just canned tuna) definitely enhances my cognitive ability. That was something I’d noticed before I ever read that it’s a known thing.
Coursera has a course called Learning How to Learn, which is more than just study techniques. They include brain research findings.
One takeaway is that the more you think about something or do it, the more connections for it grow in your brain, the larger an area your brain devotes to it. So if there is a specific ability or topic you want to improve, just practicing it, just doing it (for 10,000 hours or more, is the rule of thumb) will get you there.
Norman Doidge’s tales of people who have overcome brain damage (e.g. The Brain that Changes Itself) are fascinating and may give you some ideas of ways you might want to work with your own brain.
Edit: Meant to add, lucid dreaming is another good technique.