Overread and bullitt make good points; practice and DoF. Appropriate DoF is key to good wedding shots. In addition to requiring longer exposures, smaller apetures will give you a greater DoF (more of the image is sharply focused). This is good, right? Nope, not always. Often there is an unattractive background that you want to obscure. The best way to do this is to leave it out of focus. Spend some time learning how to control your camera.
Others may disagree, but my suggestion is to use your camera in Shutter Priority (Not sure of the Canon-ese for that) and set it at between 1/125 and 1/200. That is fast enough to freeze movement. The danger, IMO, of using apeture priority is that you can lose track of the shutter speed when adusting your apeture to get that critical DoF and wind up taking a whole series of shots at 1/30 or lower and finding them too soft to use. Better to have a little less than ideal DoF and a crisp shot.
Keep your ISO as low as you can, but don't be afraid to crank it up to get 'that shot' if you need to. Do some research/practice, and find out what your camera's acceptable high ISO threshold is.
Take an hour or two and surf the 'sites of wedding photographers; look at different poses and and styles they use; ensure you know (either from the main shooter or the family) if there are any special poses, requirements, etc that they want captured.
There are a LOT of really good wedding photographers here; I hope they pitch in.
Good luck!