This book is a collection of 50 sayings from the nine-volumes of Complete works of Swami Vivekananda. The book is available here.

Here are a few of the sayings that I liked the most from this booklet:

Followers will only follow those leaders who are ready to give up their life for the cause.
If you can't learn to obey, you cannot lead.
Great things are only done through great sacrifices.
Know that talking ill of others in private is a sin.
It is criticizing each other that is the root of all mischief.