There is the idea that you can prevent decay in cognitive function by doing inane, mindless games on the computer, such as those peddled by lumosity.
I do the NY Times Crossword most days, and usually try to use five minutes per degree of difficulty (Monday 5, Tuesday 10, Wed. 15, etc...). I do a puzzle called kenken as well. Then I compose music or work on previous compositions. I try to work on my research every day, not breaking the Seinfeld chain. I have to figure out how to teach what I know to groups of students...
I have another goal of being able to read novels in all the romance languages. That's another cognitive stretch. If someone can find me a novel in Rumanian or Provenzal I would appreciate it.
Really, though, my whole life is devoted to the cultivation of intelligence. That's all I'm about. There are two or three ways of doing this. Learning to do novel tasks stretches the mind in different ways. So I have tried to teach myself to draw, to compose music, to read Italian. Delving deeply into a subject matter that is not novel, that you know very, very well, is also good. So writing a third book on Lorca... A third way is to solve puzzles or memorize poetry.
I hate that this sounds arrogant, but if I am intelligent it is because I do these things, not the other way around. If I am stupid about other things, it is because I haven't cultivated thoses sorts of intelligences. Put me in a home depot, and I am a blithering idiot.