I would like to hear a few, if you don't mind.
Well, there needs to be much more than few, to be honest.
Small things add up to create big thing.
Like, listening to classical music is linked to increased intelligence. Learning to play a musical instrument is linked to increased intelligence. Meditation and deep slow breathing is linked to increased intelligence. Binaural/Isochronic/Nature sounds/white noise are also linked to increased intelligence.
Playing smart games where you solve logical problems is also linked to increased intelligence. Some foods are linked with increased intelligence.
Drinking two glasses of water after waking up, two glasses of water before sleep, as well as drinking water every hour and aiming for 3 to 5 liters of water per day to prevent dehydration is also linked to increased intelligence. Debating and playing chess also helps with intelligence. Learning about logic, deduction, premises, conclusions, logical connectives is crucial for thinking, so it helps intelligence. Reading book summaries of smart books (Better than reading whole books. You get best ideas much faster.), writing down important things to use them later, writing down thoughts and ideas and solutions, and using AI also develops creativity and intelligence. Reading smart things, research and statistics is also guaranteed to challenge a person and improve intelligence. Learning how to create statistics and data from large collection of facts is also good. Learning a new language is also linked to higher intelligence. Memory games, memorizing songs and singing can improve mood, which indirectly helps intelligence, as memorization practice and good mood are beneficial to a person.
But imagine if all of these were combined and used together. They would create much greater effect when combined.
I have so far created a list of over 300 things which increase intelligence, and if they were all implemented, there would basically be a guaranteed increase in intelligence. Meditation and deep breathing on their own can increase intelligence by 10 to 20%.
Some things on my list are used in US schools, but in too small amount and mostly negated by all the useless things in US schools (knowledge which is neither necessary neither improves intelligence much).
