Group interviews are the worst. There's always someone who thinks the best way to get the job is to never let anyone get a word in.
Your best bet is to be super-prepared, where you can speak with authority about the company doing the hiring and why you, in particular, are best suited for the job.
Wow. When I read group interview, I thought it was a group dynamics game, then the real interview. Have done two of these in Spain (they usually explain the group a certain problem/case, and then you have to think of a solution together without voting) and I understand they help the recruiters know a bit how your personality is. But a group interview is crazy! People already never stop talking in the group dynamics (and probably won't get recruited, as they are being too much aggressive, depending in the job). If the actual interview was done in group it would be something very scary, people fighting with each other and nonsense. But maybe that's what they pretend...
In any case, the best thing you could do is trying to be assertive. It's difficult if there is someone too aggressive, but just try to say your things the best way, and short, try to stop the people talking if they are capitalizing the time, and if you see someone has not talked yet, give the turn to him instead of using it yourself (specially if you have already talked about that particular part of the interview).
I managed to do it quite well in the dynamic groups where we were all engineers (I was one of the 4 out of 11 that actually did the private interview), and also quite good in one I was the only engineer (but those damn business-like economic guys were more difficult to argue with, and there were several of them who knew they needed to be assertive).
PS: And of course what MC Safety says, read a lot of information about the company, its position in the market / similar companies, the skills needed for the position, whatever you can dig about it. They like that a lot, for sure, and it demonstrates a bit of initiative / love for the company.