A simple short list of segmentation method best practices.
Of which determining the number of clusters is probably least understood.
See also https://communities.sas.com/thread/35557?start=0&tstart=0 for certain thoughts on using CCC and interpreting them for number of clusters.
Is CCC both a neccessary and sufficient condition for determining the number of clusters? Does this quaint nerdy question matter? oh… yes; believe me! So, how do I understand this with out getting discouraged by the mathematics of it. Visualization can help a lot, here.