When reading some of these articles I realized choosing the best one would not suffice, they are all encouraging and well written so I am just listing all of them instead.  Enjoy!

Improve your confidence: 10 ways to overcome insecuritiesBy Shonna Waters, PhD

How to overcome insecurityBy Tony Robbins

How to Stop Being Insecure and Build Self-EsteemCindy Lamothe

Three Ways to Beat Your InsecurityLisa Firestone Ph.D.

How to Stop Feeling InsecureTina Gilbertson LPC

The Key to Overcoming InsecuritySusan Krauss Whitbourne Ph.D.

How to Overcome Doubt and Chronic InsecurityPadraic Gibson D.Psych

The 3 Most Common Causes of Insecurity and How to Beat ThemMelanie Greenberg Ph.D.

Why We Feel Insecure, and How We Can StopSusan Krauss Whitbourne Ph.D.