Cisco believes that the default signature settings are their Best Practice. Unfortunately, this is not true for anyone who is performing analysis of the events their sensors generate. There is no published guide I'm aware of. Everyone with a BP signature set has whipped it into shape the hard way, by investigating each med and high severity event, (trying) to look at the signatures to determine if they're capturing what they want to see. Using the capture action will go a long way to aid in your analysis. Tuning down the noisy, false positive and un-actionable signatures is a good way to start.