Are you having a band or DJ at your wedding? Most bands and DJs will ask you for a sample list of songs you like, to give them an idea of your style and a base from which to go from, like your own personal pandora station. But, I'd recommend taking it one step further- give them a do not play list. It doesn't have to be extensive, but music can really set the mood for an event.
What to put on your do not play list? Are there any songs you can't stand? Any songs that remind you of an ex? Any genres that you'd rather avoid? Think through the last few weddings you attended, where there any moments where you thought, "Why are they playing the Pussycat Dolls? This is terrible!" or something similar. Seriously, I've heard some bad music- and with one quick little list, you can insure you enjoy the music all night long.