1. The bride and groom must be happy.
If they are happy, it is much easier for everyone else to be happy.
2. The right music is crucial- and live music helps.
Of the three weddings we've attended with live music, 2 had tons of dancing. Of the DJ or ipod weddings, roughly 25% (2 of 8, I think) had a lot of dancing. Regardless of how the music is played, it should be music that everyone, from grandparents on down, should be able to tap their feet to. Our big band played standards from the 1930s, '40s and '50s; my brother and his wife had a funk band that played classics from the 1970s through today. But in each case, most people knew most of the songs.
3. A dance floor in the middle of the room helps.
All of the weddings that I've attended with a lot of dancing had the dance floor in the middle of the room, surrounded on three sides by tables, with the DJ or band on the 4th side. This makes it easier for people who are not dancing to be part of the dance floor, and if people stop to take a break, it is much easier for friends to get them back on the floor.
4. Booze is important.
5. The bride and groom must be on the dance floor.
My mom asked me if we would go around from table to table at the reception. To her initial dismay, I said no- we were having a receiving line so we wouldn't need to do that. I said that I planned to be on the dance floor the entire night, and if people wanted to talk to me, they could dance with me. Whether it was the right thing to do or not, it worked.
Anyone have other tips to add about how to get the dance floor moving?