Automatic Reference Counting (ARC) simplifies a lot in Objective-C, including singletons. Here's a template for you:

+ (id)sharedInstance
{
      static dispatch_once_t pred = 0;
      __strong static id _sharedObject = nil;
      dispatch_once(&pred, ^{
           _sharedObject = [[self alloc] init];
           // Additional initialization can go here
      });
      return _sharedObject;
}

Source:

• http://lukeredpath.co.uk/blog/a-note-on-objective-c-singletons.html