Journal Daily
I've been writing a journal for a year and it has been one of the most rewarding habits. Initially I was skeptical and it felt weird. But it might be the most useful tool in understanding the mind.
The mind is constantly running a radio show in the background. Through journaling, I realized that I have been taking it too seriously.
The journal that you write is a reflection of what you consume. The books, the people, the conversations. It is like looking at the quality of water in a stream. It gets muddy if the input is dirty.
Even though I don't review my journal entries much, I am able to put out the 'radio' onto paper, or something outside of my mind and observe it. It is almost like a meditation practice.