Which habit do you think one must invest time to build-up on the way to becoming a good leader?

I think it must be RESPONSIBILITY habit. This word has many meaning dimensions described here:
1. First, the leader must take response for all his filling/reaction with the view that no-one couldn't force him do anything if he don't let them do that
2. Second, the leader must take response for overall result by coaching his team members achieve the goal on their own responsibility
3. Third, the leader must positive oversee something which he and his team could do to make a better results without asking from his managers & his followers.

Know yourself, courage to admit the mistake and stay positive

I did answer it here http://www.anphabe.com/discussions/ajax/answer/like/1830, post 1830, but I want to offer another impression, now that I have even more time to think.
No matter the talents, or skills, a company most often reflect and affected by its leader's personality, no matter his/her actual position. To put it more clearly, the true leader of a company has the strongest effect on the character, the personality of that company. CFO, CEO, Chairman, doesnt matter. If you are a true leader of your company you can mold your company to your way of thinking. If you are a competitive, aggressive, workaholic of a chief, god help your employees! They will get dragged along your way of working nil they will they. If you are a competitive, aggressive, oneupmanship of a chief, god help your company! It will be a place of competition of the silliest thing possible.
So think carefully. Do your company reflect your character?

Work with passion with an open mind and heart. Learn to be an effective decision marker.

If you ever seen the movies Bao Thanh Thien (don't know how to write english name :D), you can see Bao Thanh Thien as the leader in a team (include Trien Chieu, Cong Ton Sach,...). He is straightforward & make clear cut any 'business' what every one must admire! It's a perfect leader that we want to become :)