It is always a good idea to know where you are starting from. Using the Stoney Point headspace gauge (now being sold by Hornady), I first measure the shoulders on a few new cases. Then I measure the shoulders on a few once fired cases. This will give you an idea as to how much headspace you have with new brass. Not precise, but ballpark.
The measurement of the once fired cases is "usually" a good reference for where the shoulder should be on reloaded cases. I typically adjust my die so that the shoulder is about .001" shorter than this measurement. IMO, a slight resizing of the case after each firing is better than neck sizing until the bolt is hard to close and then FL sizing to minimum dimensions again.
Working without some kind of measuring device makes everything nothing more than guesswork.