The key ingredient to keeping a full dance floor is to keep the flow using gradual ups & downs using Beats per minute as a guide to creating a good flow of music. Using BPM's gives you the option to adjust the speed up or down to match the tempo of the record currently playing and a classic song that wouldn't normally work will give a new take and a whole new character at a different speed. (Plus or Minus)
Using your Musical and BPM knowledge you can maintain consistent BPM's from one song to the next, there is a smoother transition, and less likelihood of dancers deciding to leave the dancefloor.
When you have the BPM's of all your records you will be able to experiment and be different - you can come up with some truly spectacular segues and mixes that will leave the dancers amazed at your musical knowhow and imagination!