A game can help in getting people on the dance floor. Be sure to do this in the beginning of the dance evening (the moment the guests should start dancing).
A self-made game I usually do a lot to start the dance floor, is the following:
I call everyone on the dance floor, in a big circle. I start a song and wait until everyone is on the floor. This can take a while, so I keep on calling and encouraging them.
If they are all in the circle, I select an assistant and ask him/her to dispatch cups, filled with water. Usually I take 4 to 5 cups, depending on the size of the group.
In the meantime I explain the game: people are passing the cups to the person left to them. For fun, I explain there is very hot coffee in the cups (of course, there is only cold water, and they realize this immediately). This happens when the music is playing.
When I stop the music (at random), the persons holding the cups, need to move in the middle of the circle and give to cups to the next person.
After that, I start another song, and we go for another round. In the middle of this circle, dancing is mandatory.
The music goes faster and faster and I always pick funny songs. It usually takes 3 to 4 rounds. When I see there is a lot of movement in the middle, I yell to put the cups aside and the party is a fact! I never care to actually finish the game and bother with winners. If I get the majority dancing, the game is over. Mostly the people will stay on the floor and dance. Mission accomplished.