This chapter presents six principles to help decide whether a particular pronunciation problem is worth teaching. The principles are intended to begin to define what an intelligibility-based approach is like. The principles are sometimes ambiguous because no category of sounds is a priori either to be included or to be excluded in an intelligibility-based approach.  Each general category includes more and less important features.  There appears to be more important and less important consonant and vowel sounds, just as there appears to be more and less important elements of intonation or word stress. The guidelines are an explicit attempt to define parameters for informed intuition, an argument for a nuanced approach to priorities, and, hopefully, a way to have an impact upon classroom practice and help to use precious classroom time more effectively. The guidelines include prioritizing features that are explicitly connected to other areas of language use, that affect the ability to process speech, that privilege important lexical items, that carry a high functional load, that are more frequent, and that are easy to learn. Each of these principles is based both on research and informed intuition, and can help teachers to decide whether something is likely to be worth teaching.