I applied for a sales position online and was invited to a Group Interview 3 weeks later. We sat around a table and roleplayed several "difficult" sales situations. IMO, they all had common-sense solutions but some of the interviewee participants didn't do so well. My only advice in this area is to be professional and courteous. Don't bend over to any customer with a complaint. You need to follow policy but do so in a polite manner
After that, we did 3 exams (Computer Knowledge, Personality exam and IQ exam). If you built a computer in the past decade, the computer knowledge is easy. The Personality Exam is literally "don't steal". If you tolerate any form of theft, then you may not get second consideration. Even if your newborn baby steals, you gotta turn him in to the cops, no ifs ands or buts. The IQ exam is trickier but not too bad. Of all the exams, I think the IQ exam is the least important.
WITH THAT BEING SAID, I got the vibe that the overall importance of the Group Interview pales in comparison to your availability. In other words, even if you have perfect scores in all 3 exams, but you have extremely limited availability (i.e. you can't work on weekends whatsoever), then the manager may not consider you at all. I saw a lot of bright individuals in our group interview that I would have hired above me, but as far as I know, they weren't accepted. Perhaps it was due to availability?
Anyway, I got scheduled for a 2nd interview late that night and got accepted. My opinion is that if you get invited back to a 2nd interview, you're pretty much in. The interviewer asks you a few questions, but I got the vibe that it was just a meet and greet type of interview, i.e. they wanted to get to know me better as a future employee.