You might like to start by breaking down the music into sections, such as the introduction, verses and Breaks
Think about where you might like to choreograph up to as a way of time keeping. You can cut the music to this time using tools such as garage band or audacity or you can simply fade the music.
You could use your music breakdown to seperate the choreography - assigning one person to a section ect or you could work through together from the beginning to the end