Get it Right, Get Results: Plank
Planks are probably the best all-around abs exercise. They are safe, effective, and efficient. But if you do them incorrectly, you can cheat yourself out of the benefits-and possibly hurt your shoulders or lower back.
In case you're rounding your shoulders, letting your hips sag, or just doing planks all wrong, check out this video for simple tips on how to check your form-and get better results faster!