Get enough sleep. It will give you better intelligence, happiness and health.

There is existing lots of research on how very bad sleep deprivation is for cognitive performance. Many smart people are keen to get smarter by taking nootropic drugs, which have not so good evidence of effectiveness, and not much evidence for long term safety.

Not to be sleep deprived is a massive, free cognitive enhancement. Not only is it good for your cognition. The long term health effects have been studied, and it is not only not bad for you, it is indeed very good for your health. You will almost certainly live longer as well as smarter!

Many smart people also stay up late at night and get up too early to get enough sleep. This is a bad bargain. It is hard to change this habit. However, the gains are potentially very big for people.

I have changed my behaviour before big days at work when I have to appear smart. In the past I am staying up late the night before to practice and prepare. I would not prepare for such meetings by drinking alcohol, because I know it would impair my cognitive function, including how well I am able to assess my own cognitive function, so I would not perceive how impaired I was. But I did prepare for such meetings by not sleeping properly, although the effect is the same. Now I go to bed early that night. I feel I am much smarter, and have had more success recently in these big days.

I consider going to bed early is my secret weapon to get smarter. This is a trick to make it seem more fun than staying up late playing a computer game instead!