Trying for the life of me to get this video link in...
Planks can be difficult when just starting; this video demos some ways to progress. It's 5 minutes and shows four variations.
[nomedia="http://www.youtube.com/watch?v=GrHG7m4m4-A"]Plank Progression - Primal Blueprint Fitness - YouTube[/nomedia]
Well folks, it won't imbed, but the link will take you there.