The Leadership Challenge by Jim Kouzes and Barry Posner is a widely acknowledged classic that might be the most evidence-based leadership book in the world.  The foundation of the book is the Five Practices of Exemplary Leadership® Model (as also described on their website).  The five practices are:

1.Model the Way.  Find your voice by clarifying you personal values. Set the example by aligning actions with shared values.

2. Inspire a Shared Vision. Envision the future by imagining exciting and ennobling activities. Enlist others in a common vision by appealing to shared aspirations.

3. Challenge the Process. Search for opportunities by seeking innovative ways to change, grow and improve. Experiment and take risks by constantly generating small wins and learning from mistakes.

4. Enable Others to Act. Foster collaboration by promoting cooperative goals and building trust.  Strengthen others by sharing power and discretion.

5. Encourage the Heart. Recognize contributions by showing appreciation for individual excellence.
Celebrate the values and victories by creating a spirit of community.

The five practices work across settings and situations, and provide a sound foundation for experience and aspiring leaders.  We highly recommend The Leadership Challenge as priority reading for professional development.