Few things are more frustrating than being unable to get back to something you’ve been satisfied with in your work. That’s why you should save your project files as copies, while incrementing version number whenever you make some significant changes to it. Many software has this functionality built-in to save you couple of clicks.
In different software they called differently: empties, nulls, locators, etc; but the idea stays the same – to organize objects hierarchy in you scenes. Think of it as of folders in you operating system, or boxes on which you put labels and can conveniently store and transport a bunch of objects inside of them.
As obvious as this tip might seem, throughout my CG experience I can tell, that project, where everything named and organised properly is more like an exception to the rules. And that’s no surprise, knowing how infinitely lazy human beings are.