If there is one thing that made Einstein smarter, undoubtedly it is curiosity: passion to know.
This is the best brain hack anyone can ever employ to gain mastery in any field. Imaging how you would be smart at Maths if you actually take the time to study even the origin and practicality of maths. Maths itself isn’t meaningless as people think it’s nothing more than irrational jargon made rational, it would rather meaningful if this is based on some existed problems it has solved in the past. Ever wondered why Pythagoras theorem would be useful in daily life? If your answer is still “NO”, I suggest you go and find out and see for yourself.
Any intellectual domain either concrete or seemingly abstract is based on mudane aspects of everyday life. Understanding this would always boost your brain power.