https://www.creativelive.com/class/beginner-photoshop-troubleshooting-ben-willmore

Discover solutions for your everyday Photoshop troubleshooting. You will learn how the misapplication of Photoshop's workhorse functions - selections, layers, masks, color mode and more - can create problems that cascade throughout the rest of your project. Develop a mental workflow that will help you quickly diagnose and fix these issues in the future.