Beyond the settings you can access from the Preferences menu of Xcode, there are a number of configurable options that can be set using the defaults command from a terminal window.
Two of the settings that I have configured are to beep when a left bracket ( ] ) is entered without a matching right bracket, and second, to increase the number of entries in the recent projects menu (File menu, Recent Projects).
From a terminal window, here are the commands I ran to set each preference:
defaults write com.apple.Xcode PBXBeepOnNoMatchingBrace YES defaults write com.apple.Xcode NSRecentDocumentsLimit 20
You can see the entire list of available settings by reading the document Xcode Expert Preferences Notes (see the Bookmarks section in the Xcode documentation window).