How to find a (new) raiding guild

Recently, Aethel switched to another guild on another server. Here I would like to share some of my experience. It is not much different than job hunting to me. It's about matching your expectation and expertise to their need. If they have no obvious need, then it's your call to make them think they need you.

Do you want to raid? What contents do you want to see?
If you want to go raiding but you don't know about how guilds are progressing in the end-game content in your server, Wowjutsu is your answer. It records the loots from different boss kills and are rather updated.

What guild are you looking for?
Hopefully you have identified a few guilds, then you can start googling. Simply search with realm name and guild name. Most guilds have a forum or a webpage, and there you will find out approximately who they are.

Native language?
If they are written in a language you cannot understand, then that guild is off your list. If the guild speaks the same language as you, it might be good. There shouldn't be excuses of communication problem due to differences in English understanding. And people will have similar culture and values. However, the language can also be a limiting factor for progress and future recruitment.

Age limit?
The age limit can usually be found in the recruitment related threads.
There are both advantages and disadvantages.
Younger people would progress faster, raid more often but might also risk more drama and sudden quit.
Older people is more or less the opposite. However, age and maturity do not have direct relation. Read on the forum, talk to some people in that guild and go instances with them usually tells you more.

Causal or hardcore?
If you can find any links for DKP site or raiding schedule, you can see if they are active. Else Wowjutsu's loot-date would also give a hint.

Are they recruiting?
Looking further in the recruitment thread (most have), you will find the recruitment requirement and status.
If there is a vacancy for your class and your spec, that's a good news.
Most guilds accept unsolicited application, meaning that if your application is exceptional, they will consider it even they are full on that spot.

Do a brief check on Wowarmoy page and see if they have more than enough of your class. Some classes such as warlocks are extremely good grinding alts. If a guild has 10 warlocks, it doesn't directly translate to 10 warlock raiders. You will need to check/guess the ranks. The lowest rank is usually alts or new recruits. But which ranks are the active raiders? It's a guess. Most guilds have a rank for alts, so look for the highest rank with non-70s and then all the rank upward can be counted as active members.

Apply?
If you want to apply, always use their application template (if there's any). It will give a bad impression if they suspect you copy-and-paste another application. Also, some people (like me) consider it impolite and non-dedicated if one applys to many guilds at the same time.
If you have questions about anything about the guild, don't be shy and PM the officers. They are usually happy to help and answer. And you can get to feel how the guild is as well.

An extra point about finding a new realm, Wowjutsu is also a good place to start. I also recommend check it on Warcraft Census. It has some quite good statistics about the realms such as population, activity and alliance-to-horde ratio. Since I'm not a fan of ganking, I'd like a realm with more alliance than horde so I will be less-likely ganked (theorectically).