Too many cooks in the kitchen- Even if you have 8-10 highly intelligent people in your 10 or 25 man raid, it doesn't mean they should all chime in during raids. I'd love 8-10 intelligent people to theorycraft on our forums about what we need to improve, but not during a boss attempt. It creates too much confusion(oh, we could do it this way... no, but I heard on bosskillers this is the best way.... etc.) when you have 3 different strats or ideas being called out. Limit who talks in vent about how things are going to go. Receive input through tells from the other people, and discuss it in O chat.

Delegation is a great one. Tonight we had 2 rogues and 2 mages that wanted in to kill prince. I was trying to keep a balanced raid(1 hunter, 1 rogue, 1 mage, 1 lock, 1 sp) and thus had them work it out between themselves. If people can't decide, or your class leaders can't choose, get as much info from them as possible and then make a decision. Discuss it after the fact if the losing party is still pissed, but don't get bogged down by deciding every little issue.

Start and end on time- Don't tolerate people being late, unless they absolutely can't make it on time. Starting a raid a half hour or an hour late because 3 people want to finish an instance, or turn in quests, or farm while the raid forms, is inexcusable. It lowers morale overall because the other 20 people are angry that their precious time(which could be spent irl or farming or w/e) is being wasted. Then they lose faith in raids, and start slacking or showing up late as well. Key to this is having your leaders always there first, always there on time. I think it'd also help if you have extra players, so that if people go "omg just lemme kill this last boss for my badge!" you can simply get someone else. It's not too hard to start raids on time, end on time, and get people to come prepared. You just have to setup raids around the majority's schedule and then keep everyone motivated, so that they WANT to be there.

Quash Drama- Drama between players, over loot, etc., is killer. It's incredibly difficult to act in a co-ordinated manner if your OT hates your MT, or if your healers could care less about your melee dps. Not everyone has to be friends, and cliques, as mentioned before, can be dangerous in their own way, but your raid shouldn't have storms of drama running it. This is probably my biggest challenge at the moment. I've taken a diplomatic approach in a lot of cases, talking to both sides through tells or in vent. Getting people to calm down and give each other a second chance.

Be positive, but frank. If someone's fucking up, don't pussyfoot around it. But don't insult them either. And try to keep their spirits up, perhaps by saying things like "you got it this time".
Insults will just lead to resentment, long term poor performance(due to apathy: who wants to help assholes anyway?), and less receptiveness(is that even a word?) in the future.

Also, no one should take offense to screwing up. It hampers the learning process in general when you can't fix issues because a raider is in denial. In general I don't have this problem with people, but I've known others in the past who simply won't admit that they've fucked up. If they won't fess up to an issue, take it up with them in tells when you have time. Explain that you don't give a shit if they chain flame wreath, as long as they fix the problem promptly. They shouldn't be afraid of failure. They should just recognize and correct it.


Work- Despite being able to delegate a lot of things, I still find that there's so much I can improve on. Getting people's morale up for the next raid, if the last one went poorly. Making sure everyone knows our plan for every boss, etc. There's just tons of social interaction you can do as a leader that goes a long long way in creating a successful raiding guild. A lot of the tedious stuff can be outsourced if you know someone better than you at it(DKP, raid schedules, rosters, strats come to mind as examples), but nothing can replace(imo) the human element to this game. You should get to know everyone in the guild, at least on a conversant basis.

[Edit:] One last thing, before I pass out and sleep. Having a good command voice, or a get-er-done attitude I guess you could say, goes a long way. When you tell people to do something, you want them to do it quickly. Maybe not at fast as humanely possible, since that'd be asking a lot of people, especially for a game, but promptly. Part of this is you need to have authority(should be a given, as an officer/raid leader), part of this is you need to be respected(takes a lot of work, and is easily lost, so this is a pain), and part is that people need to know that you mean what you say. Being honest and forthright helps a lot in this respect, and carrying out any threats you make is another. I'm not saying threaten your raid necessarily, but if you've got a jackass in the raid, and a good raid not in it(say, who happened to be late and thus didn't get invited), the jackass needs to know that when you say "Get to Gruul's now or I'm replacing you" that you mean it. Otherwise a lot of people will totally ignore/walk all over you.