I've seen a number of posts on how to apply to a new guild. There's some very astute points from many of them. (I'm so sorry... World of Matticus is the only that comes to mind atm, but I know I've read a ton of other ones.) If you're looking to join a new guild, there's good ways and bad ways to present yourself. Please don't do the bad things.
On Monday night, when we killed Magtheridon, I get a random whisper as we're clearing trash. I was still in the process of organizing the clickers (via the old pen and paper deal) and generally telling people what to do. Long story short: even after I told him I was in Magtheridon's Lair leading the raid, he still continues to ask me a few questions. /sigh
There's a lot of information out there about a potential new guild. You can tell where they're at in terms of progression via wowjutsu or your realm forums. You can tell who the GM and officers via WowArmory. And if it's an established guild, you can probably google their name to find their web site as well. But please, please don't expect to have a full on conversation with one of the officers in the middle of the raid. I was nice to the guy, and wouldn't even say no to him if he applied on that premise alone. But come on... seriously.