I think learning the basics of critical thinking is important. This mini guide is for people who don't have a lot of time to go through the main Critical Thinking 101 post. This list should give anyone a solid foundation for critical thinking skills.
-AUDIO
*An Introduction to Skeptical Activism by Dr. Steve Novella
This is a great lecture by Dr. Steven Novella. Dr. Novella, from the Skeptic's Guide to the Universe podcast and president of the New England Skeptical Society, gives a lot of insight into skeptical activism and the basic things that every active skeptic should know. This lecture was hosted by the New York City Skeptics.
-ARTICLES
*Scientific Skepticism
This excellent wikipedia article lays out the basic characteristics of scientific skepticism and skepticism in general.