I'm going to start off with the fair warning that this is a bit of advice. I believe in things like "fair play" and "giving people a chance." If you don't care about trying to do "the right thing" or maybe even interpret "the right thing" the same way I do, a lot of my advice will simply fall flat. It is what it is, and to each his own.
Start off fair
Frequently, when I hear people say "I never agree with my raid leader!" they're talking about on-the-fly strategies and they're talking about trying to reach consensus in the middle of raid. As a raid leader myself who prizes hit 10-man group exactly for its ability to communicate informally, even in that situation, I sometimes find myself unwilling to make certain changes because I don't have time in the middle of a raid.
So before you assume that you can't possibly ever agree with your raid leader, make sure you're talking to him during a time he can be receptive in the first place. It's just playing fair; trying to reach consensus while he's busy running a raid going to be damned near impossible.
I know I can do a better job
This always sounds harsh, so I'm just going to throw it out there. "I know I can do a better job" doesn't mean anything. "I have done a better job" and "I am doing a better job" are at least something people can argue; you can compare two raids against one another and gauge different measurement points to ascertain "better."
(Quick tangent: "better" is an incredibly subjective term. I always think better "at what?" when I hear that. Better at progression? Better at having fun? The two aren't the same thing. Better at including the entire guild? You have to define "better" for it to have meaning.)
More to leading than you think
Folks often think of "raid leading" as simply being the guy who calls the shots. There's a lot more that goes into it than just being the head honcho.
You have to take care of your people, make sure morale is doing okay, monitor performance, attendance, and customize strategies against your roster. You have to make decisions about which raid instance you'll go into each night, and you need to gauge whether your raid is "ready" for each step of progression. You have to recruit, evaluate, and you have to provide feedback. You have to fire raid members. And when you do fire a raid member, you have to make sure other members don't leave in a huff. (And if they do, you have to deal with that.)
In a lot of ways, knowing the fights and making raid calls is the easiest, simplest part of the job. There are plenty of resources that will show you boss fights, and Blizzard is even adding the dungeon journal to make it easier. Every armchair quarterback with delusions of being alpha dog can look that crap up; it takes a leader to handle everything else.
What do I do?
If you've tried to communicate fairly and you truly think you can do a better job of everything, you have one choice left: Start your own raid.
Try to be diplomatic, of course. It's a somewhat lame duck who posts on the guild forums and says, "I'm starting my own -- who's coming with me?" Righteous or not, people who do that always look bad.
It feels like a jerk move to break up an existing raid to start your own, but it goes back to the proof in the pudding: If you can really, truly do better, then do it. Some people might go with you, and that's a shame for the people left behind, but it's a social game. After all, the old raid leader has the same challenges you do as a brand new one.
The caveat here, though, is that for every new raid I see start in this fashion, about half blow their old group out of the water, and the other half falters and fails. It really isn't as easy as you might think, and you'll be taking a pretty big risk.
You didn't say that your extant raid leader is doing a bad job, just that you think you could do a better one. You need to make sure you think the risk is worth it.
Ready Check shares all the strategies and inside information you need to take your raiding to the next level. Be sure to look up our strategy guides to Cataclysm's 5-man instances, and for more healer-centric advice, visit Raid Rx.