For me: diet (vitamins, algae oil, a little creatine), sleep (tracked), exercise (HIIT), reading (non-fiction - help build your vocab/mental maps), dual-n-back.
There are other tricks that I have heard of like the 'memory palace' [1], or mindfulness meditation, but those I don't think really worked for me personally, YMMV.
Have always been interested in nootropics, but I'm a dot the i's cross the t's kind of person, so haven't had anything to do with those.