fire a successful coach (success being defined by wins & losses) unless you are sure you are getting a top tier coach. You don't gamble on an up and comer (see Anae dismissal for Brandon Doman) or a successful assistant who hasn't been head coach before (Norm Chow anyone?). You go there when you are already in a high risk state (see end of Crowton era), and have to gamble to make a splash.

Don't go there unless your next Candidate is a proven better alternative (see Andy Reid).