Well, I'm not going to come on here and pretend to be an "expert"...but all of those things that were mentioned (wrist position, elbow position, etc.) are aimed at keeping your rod tip travelling along the right path. Whatever your rod tip does, your flyline will follow. If you're breaking your wrist causing your rod tip to dip on your back cast, then the flyline will follow and your line will hit the water behind you. If you're hooking your rod tip on your casting stroke, your flyline will follow and produce a crooked loop that comes in from the inside out. All of these errors will produce a less efficient loop affecting your accuracy and casting distance.
The aim of casting a flyrod is to try and keep your rod tip travelling in as flat a plane as possible. It doesn't matter whether your elbow is right next to your ribs or not, as long as your rod tip is travelling in a straight line. In fact, the more line I need to support up in the air, the longer my casting stroke becomes.
Several other factors need to be considered to make a good casting stroke. Power application needs to be precise and in the right part of the stroke. Overpowering a casting stroke can cause your rod tip to dip and flex in unusual ways causing problems such as tailing loops or line stacking. Timing is also critical. The most common error that new casters make is not allowing their back cast enough time to lay out before starting their forward cast. Take your time to learn how to make a good back cast, and this will help your forward cast tremendously.
Sometimes asking people's opinion about anything to do with flyfishing results in more than a dozen different answers. And in this way, sometimes I feel sorry for the beginner for all the confusion.

There are some really good certified instructors that I've heard of. Scott Baker is certainly a good one out of Angler's West, and so is Brian from Whistler Flyshop. Those guys can claim to be experts...and their opinions probably worth more than mine. Give them a shout. Scott's really friendly and approachable, and loves to talk fishing all day.

I think in the end, you will be glad that you had some good instruction in the beginning rather than learn bad habits that will be hard to unlearn later.