Playing Music For The Dancers
These guys know that most of the people don't come to sit. These DJs play the music that keeps the dancefloor packed.
Letting The Songs End Completely
For these types of parties, great DJs know that the songs need to have an end. It can be frustrating when one song gets mixed into another and the couples just keep dancing. Sure.... they can just stop dancing, but a lot of people I've talked to find it awkward to stop in the "middle" of a song. I think there is a fear of seeming rude. When the song ends, people can say thank you and part ways, or make a joint decision to stay on the floor. Either way, there is no miscommunication.
Giving The Dancers Variation (fast, slow, etc.)
For me this applies to the salsa selections made by the DJ. Everyone has a different mix of their favorite songs (old school, new school, fast, slow, etc.). Varying the genre and speed of salsa songs during the night gives everyone a chance to enjoy the music in their own way on the floor.
I hope that others will post their opinions about what makes a great party; whether it be DJs, dance space, lighting, etc. I think anybody organizing a latin dance event will either benefit from the feedback and/or see how things that may seem so small can make such a big difference. Thanks for reading and keep dancing.