While conducting a focus group can appear very similar to sitting around and chatting about something, there are guidelines that make it more effective, valid and reliable as research.  The attached methods guide from the University of Reading (United Kingdom) is a good short introduction and suggests further readings. CILMAR's assessment expert is also very fond of the Focus Group Interviewing website  (and books!) of Drs. Richard A. Krueger & Mary Anne Casey, who have over 40 years of experience & with whom she considers herself extremely fortunate to have studied.