Put your best foot forward: Before you begin applying to a guild, make sure that you have your best gear equipped and that it is visible on your Armory page. Much like wearing that Sunday suit to an interview, this shows the guild that you are serious, and gives them a status on the amount of effort you have put into preparing to raid. Also, if the guild requires you to be a free agent before you apply, make sure that your Armory page also reflects that you are no longer in a guild. This might seem a little odd, but look at it this way. Raiding is a community, and despite being highly competitive, raiding guilds are also fairly respectful of one another. They don't want to poach players from other guilds. It makes them look like loot ninjas (toon ninjas?) Plus, if you are fishing around and applying to their guild while still in another one, chances are you are going to look like you aren't interested enough in becoming part of the group. Do yourself a favor and /gquit enough in advance that you avoid this headache before it happens.
Read everything: When you write out your actual application, make sure to read everything twice before you actually start filling out any forms. I say this because some guilds will ask that you post a new thread in the guild recruitment forums, and some will be sneakier and toss in an extra set of instructions to see if you are actually paying attention. Like, for instance, requiring you to get a sponsor from the guild beforehand, or sending your guild application in a private message to one of the officers. The application is your moment to shine, so make sure to copy and paste the application into a word processor and fill it out there. Use whatever info is applicable from your pre-made application and use spell check. I repeat use spell check. This does not mean check your list of spells. Save yourself a copy and note when you applied to the guild somewhere on the file, for future reference.
Keep tabs but be patient: Some guilds will want to pick your brain about how you play your class, so make sure you check back with the guild website often to see if there are any updates on your application. This does not mean, however, that you should hound them with daily messages demanding an update on the progress of your application. This is a sure fire way to piss off those who decide things, and chances are they will reject you on principle. If you haven't heard anything in a week, that might be the time to drop them a line or a message in game and ask them if they have made a decision. This will remind them that you are still interested but show you have respect for their process.
Don't apply to a bunch of guilds at once: One secret no one will tell you is that guild leadership is a small community, and they keep tabs on one another. The raiding guilds on your server are keenly interested in what is going on with their rivals, and will know who is applying to them and so forth. So make sure that you apply to one or two guilds first, and then if you are not accepted apply to another and so on. Having a bunch of applications open with guilds is a lot like having a bunch of credit cards open: it's reflects badly on you.
Let honesty be your policy: When it comes down to it, just telling it like it is will be your best bet. Any guild worth their DKP will appreciate you being upfront and honest with them. If you are only interested in tanking, but the guild is looking for healers and asks you to respec, be brave enough to tell them so. Perhaps you've built all your gear in one direction, and would be less effective with a new set of talents. Likewise if you are applying to more than one guild at the same time, make sure you mention this in your application. Hiding this fact can seriously harm your chances with either guild since they might take this as a sign that you would hide other things from them.
So, if all goes well, you apply to that uber guild you've been dying to join, and they have seen you as a worthy applicant and accepted you. In order to survive your trial period and transform yourself from a scrub to a core raider, there's plenty you will need to know. Look for our Learn2raid list of essential raiding terms when next we meet.