Some things which help are:
~getting enough sleep
~keeping your heart healthy because this improves blood circulating to the brain.
~healthy diet (Mediterranean, olive oil, nuts...)
~caffeine 200 mg to 400 mg daily!
~Exercising the brain works. Learning to juggling is one of the exercises that was suggested.
That's why I'm learning to juggle. One ball was easy. I'm starting to juggle two balls but I still drop them most of the time. It's taking longer than I thought but I only have myself to blame because now I only practice for about two minutes a day. I'll have to put more effort into it.
Read more about the benefits on this link:
Juggling Makes Your Brain Bigger
Instructions on how to juggle are on this link:
Learn How To Juggle