This probably falls under the category of "too obvious to be worth mentioning", but I'll mention them anyway, because they're all probably more significant then anything on your list. I would say that the biggest things a person today can do to upgrade his mind are:
Education (including self-education)
Exercise:
There's a lot of evidence accumulating that regular exercise significantly improves intelligence, memory, and learning, in the short-term, medium term, and long term, in a wide variety of ways, and that it also delays cognitive decline and memory loss later in life.
Actually, that's probably true of anything that improves your heart and lung health, by improving your brain's supply of oxygen. I know that there's been recent a study that people in their 40's who smoke tend to have worse memories then people the same age who never smoked.
-3. Getting enough sleep.
I agree with putting education as #1. For the #2 slot, I'd say it's a combined Nutrition/Exercise/Sleep "General Health." All three of these feed into each other, resulting in synergistic improvements in your entire body functioning. This includes your brain and mental performance.
I've been in the bay area for a week, and already I've heard so many tips and tricks for becoming smarter that I can barely keep track. I think this is a very good thing. If effective altruists and rationalists can become smarter, then it should improve the probability of favourable far-future outcomes. Note that:
1) cognitive enhancement fits with the ideas that you will achieve most of your impact in your middle age, and that increasing your career capital is integral to achieving impact.
2) it might be possible to reinvest returns from cognitive enhancement by doing further research into cognitive enhancement. This is not to say that an intelligence explosion could occur within a human substrate - our capacity to alter our neural structure and thinking speed is likely to run up against hard evolutionary constraints in a way that machine intelligence will not. Nonetheless, cognitively enhanced humans could have an advantage in the creation of a friendly AI team.
I suggest that we collate our mind hacks here. Then we can vote them all up and down. This will generate a list of 'top rated posts of all time', which could give hints for curriculum design to organisations like CFAR. Here are a few suggestions:
Of course, if something is less plausibly obtainable than transcranial magnetic stimulation, then it won't get any votes at all and doesn't meaningfully belong on this list (e.g. deep brain stimulation, brain-computer interfaces)