[Dianapak]

Yeah, some puzzles or logic problems

[Maality]

Learning a new skill, engaging in puzzle game, listening to music, engaging in productive group discussion can all keep your mind active and sharp. Improving knowledge through online studies can at the same time upgrade you to face the new challenges ahead.

[Annalice]

try to read more psychological book

[Stillski]

Learn new things. Listen to music, try out puzzles. Read books or listen to audio books.
Try cooking. There are so many things out there to do.

[Feat]

The best thing to do in your spare time(in my opinion) is to try and learn something new.

[Zerkaa]

Solving Jig saw puzzles, Rubik's cube are some of the common strategies to keep your mind engaged. Better solution will be to have some productive work done and avoid being idle. Reading books, drawing, painting, learning new skills all can keep your mind occupied and active.

[Jeopar]

Listen to audiobooks. Explore which interests you.

[Caesal]

If u r doing any work, u have to start thinking how we can be creative, unique from others, how can we develop it. Think out of the box, u will end up keeping your brain active.

[mothered]

How to keep my brain active

Limit your exposure to TV and do something creative and most Importantly, challenging.

[Brownn]

Oh I think that you need to try puzzles for sure