Synchronizing music to movie-help

Can anyone please help and give me tips on how to synchronize my movie to music?, for example if I wanted lip movement to synchronize with the odd lyric to a song. I just can’t get my head around this… how do I know when to make a quick flash effect synchronize to a beat in a piece of music? As I am creating the animation how do I time it to the sound? ANY SUGGESTIONS WOULD BE GREATLY APPRICIATED!!!