Before you can decide what to do for your stop motion music video, you need a song. A shorter song would be easiest. The song I used was over 3 minutes which made it quite difficult. A faster, more upbeat song will be easiest. http://songza.com/
is a good resource for finding a song. They use a music concierge system to find songs based on your mood/current activities/enviroment. Picking a song can be a long process and your song choice might change a few times throughout your planning based on your ideas.