When I worked for the Texas Dept. of Economic Development- Tourism Development, we organized focus groups for new advertising campaigns developed by our ad agency. We had two different groups on three days. About 12-15 people participated in each.
The focus group was structured with a facilitator. First, the participants were told in general what they were going to see and what they were to do. Each focus group was shown the exact same materials in the same order.
The participants were members of the target market, so they were asked to write their comments about each spot or ad, so they could discuss them afterward. Then we would show TV spots and pass around print media (magazine ads). We filmed them so we did not have to keep notes.
It was kind of cool in that we were testing a new TV spot that featured Lyle Lovett. The director of our agency had already okayed the spot and Lyle Lovett had recorded the spot. We were kind of doing a focus group after the fact. It was good that everyone liked it!
The participants received coffee, cokes and ice water. After they saw the spots or print media, the facillator when around the table and asked specific questions of each person. Then the participants were allowed to comment.
They received a $50 check for 2-3 hours of work, I am not sure if they received travel expenses. This was in 2000, so the price has probably gone up.
I know that web conferencing has enabled focus groups online and they would be held in the same way. The main thing is that the facilitator explains the process, without giving hints as to what the outcome should be. Each focus group should be faciliated by the same person, if possible. Filming or recording the focus group is a handy way to capture comments that might otherwise be lost.