I'm surprised meditation hasn't been mentioned yet.
Meditation drastically boosts focus and increases awareness, which then accelerates learning of whatever is being observed / studied.
Because of this, focus is a prerequisite for learning, and learning is a prerequisite for intelligence, so focus is very important and more beneficial than many realize.
Meditation is awesome, though I don't do it enough. It's like push-ups for your brain. You just focus on your breath, and if you can do that, you can focus on anything regardless of how boring it is.
Meditation drastically boosts focus and increases awareness, which then accelerates learning of whatever is being observed / studied.
Because of this, focus is a prerequisite for learning, and learning is a prerequisite for intelligence, so focus is very important and more beneficial than many realize.