Toastmasters - Besides being a great confidence builder, the interaction of the group teaches how to work with others and encourage them, plus you can develop your skills to speak to any size group and to be quite skillful at getting your point across. Highly recommended.
BOOKS, PRIMARY AUTHORS AND LEADERS IN LEADERSHIP
If you truly want to become a better leader, these leaders are some of the very best guides. You can read lots of books by a lot of good experts, but these cover all the key points and do an excellent job.
John C. Maxwell