Pick a Range of Activities
Consider certain passive and active activities that exercise your brain and functionally make you a lifelong student. Pick up a new hobby. Take a class. Build things.
Want another approach? Develop a part of your brain that you may not be using as much. Practice writing with your other hand. Learn to play an instrument.
Learn to be an active user of your brain. Start by reducing or eliminating the most passive of your activities, such as watching TV; it’s mostly receptive and not very good for exercising your brain, unless you’re interacting with the program in some way. Plan your activities, and envision various scenarios. Break the monotony in your activities; instead of a routine, force yourself to choose differing options in your activities.