I read this book recently, it was in the library and looked interesting - it was. Seems we (humans in general) overthink everything and often we're wasting our time.
It suggested to me that snap judgements work best on things that should be obvious - if you think about rating jams (jelly in the US?) your opinion doesn't match the experts who should know whats best, but when people trusted their instincts it was much closer. We also have lots of experience meeting people and it's perfectly possible to judge someone based on first impressions (love at first sight? Why not!) but of course they could be acting so be wary on that one... As to how to listen to it you just do - if a thought hits you instantly say or act on it, you may well be right.
It's not a big book so read it if you can.