NSString *hasCompletedFirstLaunchKey = @"kHasCompletedFirstLaunchKey";
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if (![defaults objectForKey:hasCompletedFirstLaunchKey]) {

    //first time code goes here

    //set the key to yes
    [defaults setObject:@YES forKey:hasCompletedFirstLaunchKey];
    [defaults synchronize];
}