(in no particular order)
1. play a variety of music. top 40 is okay, but only if you intersperse it with other cool dance music. dubstep is fun to dance to for like one minute. more than one dubstep song=bad idea. also not really that fun to dance to for longer than a couple minutes: rap. but, there are a lot of options. throwback is fun, songs everyone know can be fun. playing music not a lot of people know is cool IF it's good to dance to still.
2. NEVER have seating available in the dance room. if there is a couch or chairs, people will sit there and ruin the vibe of the dance party. if you want to give people a place to lounge, put furniture in another room or, weather permitting, outside where guests can take a break from all of that energetic dancing they've been doing.
3. make sure it's not too light. a dance party with too much light is too much like a stake dance. and, not that stake dances don't have a very important role to play in mormon culture (like helping us to understand how awkward, but also strangely invigorating, slow dancing can be), we typically want to avoid comparisons to a stake dance. maybe you've been wary of turning out the lights in the past--sometimes bad things happen in the dark. but, a darkened dance floor doesn't of necessity lead to heightened promiscuity. but it does lead to heightened dance-ability, AM I RIGHT? (that one's for meredith and jesse:))
4. bump that music! dance parties are meant to be loud! if you can hear the person next to you talking at a normal volume, or rather, in his or her "indoor voice", the music needs to be louder. it doesn't have to be "the-neighbors-are-going-to-call-the-cops-on-you" loud, but you've got to give people a chance to drown out the stress and worry of their day. isn't that what dance parties are for, to forget about real life and just dance like no one is watching??
those are my tips, based on simple observation and not any sort of expertise. but i hope to attend many fun dance parties in the future!