[treya]

1) Think hard about things that you have to work at in order to understand 2) Engage in exercise that regularly includes anaerobic intensity 3) Sleep well and deeply

Learning is brain growth that occurs as a result of thinking, largely during rest and sleep following the activity. Exercise will increase the amount of growth that occurs (mentally and physically), and good cardiovascular health is effectively the same thing as good brain health

And, maybe obviously, practice the brain teasers and interview questions. They are a skill that is not the same thing as being mentally sharp