I agree with all the tips from PureJammy, except I'd like to add a couple of things. Talk to the couple, and ask what it is that THEY want as a wedding video. They are the ones getting married, and they are the ones who have to live with what was shot. I shot both of my brothers' weddings, and both were very different as they both have different tastes. And listen to them ONLY, and not the parents of the bride OR groom!! lol
Believe me, that's just an invitation for disaster!
It's the couple's special day, and they should have what they want.
Also, some people may not want every single second of the wedding shot, and and as in the case of one of my brothers, the video was just a nice montage of the three days with close friends and family at the reherasal, rehersal party, the wedding, and the day after, all to music that they loved. It worked really well, and the only dialogue is from the reception speeches and dinner. Also try and get the closest friends and family to give their well wishes to the couple on tape in secret..it's a nice surprise when they watch the video later on.
Have fun!!