Most dance music is based on 2/4, 3/4, or 4/4 music time. In 2/4 and 3/4 time the first beat of a bar is emphasized and can be clearly heard in the bass = drum, bass or bass guitar. This is the beginning beat of the music and is the beginning step of the dance.
In 4/4 time the most emphasized beat is the first beat and there is then less emphasis on the 3rd beat. Again this can be clearly heard in the bass instruments.
As always, the first beat is the beginning step of the dance. In some music the bass instruments will play every beat in the bar. Listen to the music - you can hear and feel the beginning beat of the bar and go from there.
The most important thing to remember is to move to the beat - listen for the bass instruments and they will show you the way.
Remember there is nothing worse when dancing than to be "off the beat" -- so listen and enjoy!