Play Games: Sudoku, puzzles, crosswords and word searches are best games to stimulate your brain
Enroll in an activity: A music class or a baking class, anything new that involves learning will keep your brain healthy
Make new friends: Meeting people is important. This will help you socialise and make new connections. Mixing with positive personalities and talking to them will help you deal with loneliness
Read and discuss it: Reading is a best therapy and a way to keep your mind active with the story. Moreover, when you are reading, later also discuss them with someone you like to talk. This will help you consolidate what you have read
Meditate: Bringing peace and balance to the brain is important. 10 minutes of meditation in a day will help you stay mentally active