Exercise. It does wonders for your energy levels and your mental well-being. Plus it will make you feel you having done 'something useful' by the end of the day. The hardest part is getting out and starting - once you are busy, it is fun.
Otherwise, reading. If you have enough energy, read literary classics or non-fiction, the type that challenges you and/or teaches you new things. If you don't have enough energy, read something lighter - I am reading Alice's Adventures in Wonderland currently, for example, which is fun and relaxing. Finishing a book is a nice feeling, plus the mental focus on the story and on yourself can give rise to some nice insights on yourself, people, and the world.
Otherwise, reading. If you have enough energy, read literary classics or non-fiction, the type that challenges you and/or teaches you new things. If you don't have enough energy, read something lighter - I am reading Alice's Adventures in Wonderland currently, for example, which is fun and relaxing. Finishing a book is a nice feeling, plus the mental focus on the story and on yourself can give rise to some nice insights on yourself, people, and the world.