1. Make the dance floor your center stage.
The bride (and groom) might be the center of attention, but the dance floor's the center of the party. If you hide it around a corner, in a separate room, or at the very end of a long hall, it's going to be difficult to pack it. Also, guests might miss or feel left out of traditions that usually happen on the dance floor, like the cake cutting and bouquet toss. Easy access to a central dance floor makes for a much more involved crowd.
2. Keep the dance floor small.
Consult dance floor sizing charts, and don't let your venue convince you that bigger is better. Adjust size according to guest number. If the floor is too large for the party, it will look sparse no matter how many people are dancing, which discourages joiners and makes party pics look lame.
3. Place the DJ right by the dance floor.
This sounds obvious, but some people (or venues) try to put the DJ in a corner. Your DJ's job isn't just to play music-it's to motivate your guests to get (and stay) on the dance floor. DJs need visibility to gauge the crowd, and they need to be able to interact with guests. You wouldn't dream of putting the band in a corner!
4. Don't position tables right by the speakers.
If your DJ's in a corner, there's usually a table (or more) between his speakers and the dance floor. So there are two options: either the music is way too loud for the guests seated at that table or way too soft for a happening party. The dance floor itself can act as an excellent buffer between seated guests (especially elderly ones) and the speakers.
5. Arrange tables thoughtfully.
Before you stress about who sits with whom, consider the arrangement of the tables themselves. Ideally none is too far away from center stage (aka the dance floor), as visibility and access are important. If you can, arrange tables in a "U" around the dance floor, with the head table opposite the dance floor from the DJ. And if you have space, a few cocktail tables by the bar will encourage guests to mingle.
6. Consider how people will move through the space.
Guests need to be able to move around comfortably if they're expected to circulate and get up to dance. Don't make them squeeze and pardon their way onto the dance floor! Do make a clear path directly from the entrance to the dance floor. Also think about the flow of foot traffic to the buffet, restrooms, and bar. If you put the bar right by the door, people will congregate at the entrance.
7. Cluster all the fun stuff.
You may be tempted to spread out the bar, the cake, the photo booth, the lounge area, and whatever other fun stuff you've planned for your guests. It might get guests to circulate, but you don't really want them circulating too far away from the dance floor. The last thing you want is a packed floor to disperse to the other end of the room to watch you cut the cake! Plus, you want your guests to interact: the drinkers with the dancers with the photo geeks, so locate the "fun stuff" together.