Your integrity is the one thing that you have complete control over. It defines who you are and affects how people perceive you.
One of the easiest ways to maintain your integrity is to follow through on your commitments. If you commit to doing something, then carry it through to completion. Not responding, showing up late, or cancelling a meeting due to another opportunity does not show respect to the people that you have committed to.
When you begin to focus on integrity in your personal and business life, you will become more protective of your time. The more you can define what you can or can't do, then the better you can define your value to others, particularly in an era when people are already over-committed and over-extended.