I worked a wedding a few years back and the newlyweds had a great idea. At the entrance of their reception there was a display with pictures of the couple as well as a jar that said "what's your favourite song?." The guests were invited to write their favourite song on a piece of paper and toss it in the jar. Then, once dinner had started someone dropped the jar off at my table and I had insider information on my crowd!
This is a great idea for a couple of reasons. Obviously I had a bunch of songs ready that I knew people would enjoy, but based on my DJing experience I could tell what other songs would work well with their picks. It took a lot of the guess work out of my job and we had a packed dance floor all night. I do in-depth interviews with my clients to make sure we arrive at your event knowing what kind of music you'd like to hear, but this small addition meant I also knew what the guests wanted to hear. It's a sure fire way to get the dance started off on the right track. Give it a shot!