I've attended a number of gangbangs in my time and there's only one path to success
1. Push your way forward. Ignore all the other men.
2. Take your time, draw out the fucking and go for as long as you can. Ignore all the waiting men.
3. Once you've come, repeat steps 1+2.
Seriously, at every gangbang I've been at, there's a couple of these types. If you're not, then as vt said you'll be spending most of your time standing aside watching the action. When it's finally your turn, you may not be hard anymore. And even if you are, you may not enjoy fucking while the bulls are snorting and waiting for you to finish.
I've had some good experiences and some bad ones, just like 1 on 1 punting. It's not for everyone, go with the right attitude or because you want to experience it once.
I believe Bethany37 is planning something similar in Norwich.