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.
*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.
This excellent wikipedia article lays out the basic characteristics of scientific skepticism and skepticism in general.