Holding the standard plank for ten seconds or longer is useless according to Dr. Stuart McGill. Unfortunately, many people still try to do planks for time.
A better way to progress this core exercise? Make it harder. The cable plank press will help you take your core strength to the next level, and you'll even build some extra upper-body muscle.
Are you doing any dips variations? You should be. Here are some interesting options, including straight bar dips and Korean dips, to jazz up your training.