Switch hands: Use the opposite hand for, say, writing your name or brushing your teeth. Does it feel weird? Awkward? It should. Your brain is learning something new and getting stronger with it.
Think about it: You can think about exercising a part of your body and help your brain improve its ability to signal muscles to act.
Experience something new: Do something you've never done before, such as learning to play chess or enrolling in a yoga class. It gives the brain a good workout.
Travel: Getting away from your usual routine and experiencing new places can help stimulate your brain.