Follow the customers. Hopefully you have thought about customer desires etc before production - that provides a starting point.
Yeah for sure! At least I try to do this. It's that framing that I use when starting the competative search. Still, too often and well after I've launched, I find myself discovering significant competitors I wish I'd known about. Also sometimes it's hard to know what keywords customers will end up using -- which is often the source of my missing competitors I end up caring about.