Xcode 6 brings a number of significant improvements. One of the more notable advances is view debugging. Often times, an app's user interface will not behave the way it's expected to. Views may not be shown or, if they do show, they may display incorrectly. This tutorial outlines how to use Xcode's new view debugging features to easily identify and fix issues in an app's user interface.
Source files for the Tuts+ tutorial: View Debugging in Xcode 6
Read this tutorial on Tuts+