1) Meditation to get my mind in check
2) Fitness/Diet, making sure I'm at an appropriate weight and fitness level
3) Sleep, shouldn't require any explanation.
Having these 3 things in check is the equivalent of 10+ IQ points. The last two items shouldn't require any explanation but Meditation is one that people often have issues seeing the value of.
For me meditation does 2 things,
1) it allows you to master the art of "staying in the zone". Lots of meditation is just accepting that you mind has many thoughts at once, acknowledging them and continuing on with what you are doing.
Once you can master the art of acknowledging your thoughts but not letting them disturb you, it lets you maintain a flow state in the real world.
I can now get interrupted and almost without fail immediately get back into a productive work state.
2) I've noticed that as I get older that most of what makes a person look smart in a conversation is that they've already had the same conversation and thought through their opinions.
When mediating on an idea, its very similar to having these conversations about ideas. You get to flesh out your ideas by having this conversation with yourself. It's an invaluable took to have.