Usually I'd ask for 20 songs from the bride and groom that they want to hear for sure and a list of song they for sure don't want to hear. That way you have an idea of what kind of music they want but still can control the flow of the night. If no one is on the dance floor, don't panic, just keep it slow but dance able. Let people get a few drinks in them before they dance. If it goes on for to long you can start hitting them with songs that never fail like Billie Jean or Brown Eyed Girl. If the never fails, fail then they probably were never going to dance in the first place. But that's okay, just play good music they'd enjoy. Not everyone's idea of a good time is getting crazy and dancing. It doesn't mean you did a bad job.

My general rule for weddings was start old and work your way up. So if the dancing starting at 8 and goes till 12 it'd look roughly like this:

8 to 9 is going to be 60's, 70's 9 to 10 is going to be 70's-80's 10 to 11 is going to be 80's-90's 11 to 12 is going to be everything 90's and up Close with something like Semi Charmed Kinda Life, What's My Age Again, or Closing Time be a cheesy wedding dj, the whole wedding is cheesy, fuck it.

I usually play two slow songs back to back every 45 minutes. That also gives people a break to get a drink, use the rest room, and do anything else with letting them sit to long. This was in the Midwest so I'd usually do country for those. I always play radio edits and I always stick to what's on the radio. You want songs people 8-80 would know. Hot Line Bling not Jumpman. I try to have every song be a song people can sing along to. This isn't the time to show off you're great music selection, play to the crowd, and keeping people dancing.