Using a second camera makes a HUGE difference to the video. Beg steal or borrow one if you can. With just one camera there is very little you can do to cover up camera movements during the ceremony and speeches without lots of cutaways. During speeches it helps to be able to film the person speaking as well as being able to cut to peoples reactions. You can't do this with one camera.
Try to plug into a sound desk where possible for the ceremony and speeches. You can't have good video without good sound.
Get lots of details of flowers, decorations, interiors and exteriors of locations. Film people having fun, smiling and laughing.
It's hard work but most weddings follow a similar pattern. Once you crack it, you're in business!