Thanks for the email- good question.
Your right- large groups are much tougher. Sometimes you start wondering if a smaller group ain't such a bad idea! :)
First- you need a lot of staff. Sometimes we forget the importance of building a staff team to help us. But we should always be pro-active about getting staff so we can keep a good staff to student ratio. If a perfect world, I like a 1 to 7 ratio. Go to my HOW DO I ...?
page and scroll down to the article about recruiting volunteers.
Then- you need to know how to handle larger groups- including discipline problems. On my ASK JONATHAN
page you can scroll down through the past questions people have asked me- there is a question titled "Kids won’t shut their big yappers!" Check out that article- it will give you some good insight as to handling crowds.
Then you need to understand programming. Because with a larger audience, dead time on stage really affects you- before you know it they're all talking and not paying attention. Check out my SEVEN DEADLY SINS OF GAME LEADING
on my game page. My book goes into much more detail about these, giving you examples of ways to do it, and ways not to: http://www.thesource4ym.com/book.asp
Lastly- also on my HOW DO I ...?
page is an article about programming for large audiences. This article deals with audiences of even 1,000. But it has some good principles. Again, my book goes into much more detail in this area.
Hope that helps.
The Source for Youth Ministry