The Four Principles of Human-Centered Design.

1. People-centered:

Focus on people and their context in order to create things that are appropriate for them.
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2. Understand and solve the right problems - the root problems:

Understand and solve the right problem, the root causes, and the underlying fundamental issues. The symptoms will just keep coming back if we don't! 
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3. Everything is a system:

Think of everything as a system of interconnected parts. 
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4. Small and simple interventions:

Do iterative work and don't rush to a solution. Try small, simple interventions and learn from them one by one, and slowly your results will get bigger and better.
We must continually prototype, test, and refine our proposals to make sure that our small solutions truly meet the needs of the people we focus on.