Many years ago I compiled a list of Xcode tips on this page. Apple's release of Xcode 4 made those tips obsolete. Around this time I discovered that using my blog for Xcode tips made more sense. I could tag posts based on a specific Xcode version and add a search field to make finding tips easier.
The link to the blog is on the site map at the top of the page. The Xcode tips are in the Xcode category. The following list contains the most widely read Xcode tips from the blog:
Most of the tips are tagged for a specific Xcode version, such as Xcode 4, 5, or 6. But many Xcode 4 tips also apply to later versions of Xcode. The specific Xcode version usually indicates the earliest version that the tip applies.