The most important habit I've formed in the last 10 years of forming habits is meditation. Hands down, bar none.

Meditation has helped me to form all my other habits, it's helped me to become more peaceful, more focused, less worried about discomfort, more appreciative and attentive to everything in my life. I'm far from perfect, but it has helped me come a long way.

Probably most importantly, it has helped me understand my own mind. Before I started meditating, I never thought about what was going on inside my head - it would just happen, and I would follow its commands like an automaton. These days, all of that still happens, but more and more, I am aware of what's going on. I can make a choice about whether to follow the commands. I understand myself better (not completely, but better), and that has given me increased flexibility and freedom.