For a start, you'll never really find a raider on the street. Given the choice, most people would stay in and do a few instances than go out for a random walk, especially considering what sporadic weather we've been having recently. Raiders like to raid constantly, for huge blocks of time at once. This doesn't mean that raiders don't have lives. Most do, but they seek self-satisfaction more than your average human being. This means that whatever they do, it's probably a means to an end. They are powered by a natural drive to achieve, which is something all guilds should look to capitalise on. I've spent more than seven thousand words talking about how to motivate your members, but these guys only need a specific goal to get themselves in the mood. That's all you need. Give them the gear and tactics, shove them in a dungeon and they'll plough through it in no time.
Or so you'd think. In fact, these folks are more likely to squabble over the basics than your average player. Take a look around your server. How many raiding guilds are there? Fifteen? Twenty? More? How many are actually making progress at a substantial rate? Five? I will never say that the people who join these establishments are not true raiders at heart, but they seem to lack the brain capacity to really put their dreams into reality. You should never encounter such idiots in your own guild if your screening process is thorough enough, but always prepare for the worst. Their mum could have filled in their application form for them, and their dad could have fluked his way through the TeamSpeak interview. Hell, most guilds only have one of those types of recruitment methods, so it;s statistically likely that you'll end up with a total moron once in a while. Identify and kick. Just don't assume that someone who makes a mistake is likely to cause more trouble. You should know when someone is constantly buggering up and how to get rid of them.
Even folks who have proved themselves to be able in the past may turn out to be tossers once they join your guild. We all know the guy who is just a little too hardcore. If they were a Pokemon, they'd be Gyrados; angry and overpowered. He knows all the tactics and is more purple than a gay rights parade, but is all too quick to remind the rest of the guild of his awesomeness at any opportunity. It's almost as if he's sacrificed part of his humanity in exchange for being a pretty good player. Some people refer to blokes like this as 'cocks'. Others call them 'dedicated'. I brand them as unproductive. When you end up having to sacrifice morale for these blokes, then kick 'em out.
Once your guild has been going a while, a natural hierarchy will develop within the raiders. There's the lower tier of players, who you drag along to Naxxramas to gear up and get them used to a raiding atmosphere. Then there's a middle tier, where members have some decent epics and know the tactics on most bosses. Or claim they do. These people should make up the majority of your guild, and the skill and gear of the people you recruit should scale with your progress, in order to sustain that progress. When you get people joining who are above the current standard in your guild, you encounter problems. They are used to raid groups that probably don't wipe as much as yours do and have grown accustom to members who know exactly what they're doing. Some of this higher tier are polite and sympathise with the woes of a growing guild. These kind-hearted souls will stick around to help your own guys get up to his standard and therefore improve everyone's life. Unfortunately, most of these more experienced players will simply leave when they realise you can't keep up to their high expectations. You must stoke the fire that warms the heart of every raider, but the more progress they've made in the past, the more coal you're going to have to pile on those flames. Otherwise, they'll proudly point out how superior they are to you and abruptly leave. You don't gain anything out of that, so avoid recruiting people from the higher tiers unless you're very close to nearing their level of experience.
Utilise the natural drive that all raiders have. Once the ball starts rolling, it will take a very long time to stop. This means you must be dedicated to such a cause from the moment you down your first boss. Get into their hearts, and inspire them to fight using their heads. These people are probably just like you, so tie in your own goals with theirs and bond together to make progress.
Raiders are special. Not in a retarded way; they're just passionate about what they do.
They may be a tad sensitive about why they raid. I know a couple who argue all the time, but work together perfectly if you stick them in front of a large monster. They use it as a way of bonding. Or taking out their frustration. All the same, best to keep out of such complicated psyche.
Be wary of the occasional idiot slipping into your ranks. When you spot one, kick them.
Fend off people who consider themselves too good to be in your guild. Their constant whining will do nothing but drag morale down. It's never worth the slight hike in DPS.
Collect momentum. Sometimes a successful guild will continue to motivate itself, given the right circumstances. Good vibes are all you really need.