1) Reading books about a wide range of topics, even though they are not directly related to my tasks at work. My exposure to French and linguistics are not related to software QA or managing a team, but it has improved my communication skills and how the usage of language is used in everyday situations (e.g., politics). Reading improves your comprehension skills too.
2) Proper diet and exercise. When I started my career, I instantly transformed into an overweight yuppie. Surprisingly (or not surprisingly), changing my diet has made me more mentally aware and less tired. When I turned 30, I started exercising even though it is something that I couldn't imagine myself doing. I once thought that the experience will just make me more tired, but I experienced the inverse: I was more energetic.
3) Mindfulness and yoga. Recently, I started reading books on Zen Buddhism and minimalism, and attended yoga classes. Truly living in the present moment and eradicating clutter (both physical and mental) made me focus on my current tasks and it made me more thankful of the things that I normally take for granted. In the end, I am generally happier. https://medium.com/@stevenom/8-lessons-i-learned-from-trying-basic-yoga-classes-70446151f17a#.6ijkcq9y2