When you are doing a plank, there are a few things that you want to make sure of in order to ensure that you are doing the move correctly. First, your body should be in one straight line from your head to your heels - no sagging in the middle or arching in the back. Secondly, be sure to engage your core muscles throughout the entire move - don't let them relax at any point. And finally, don't forget to breathe! Holding your breath will only make the move more difficult and increase your chances of getting fatigued quickly. If you can keep these three things in mind, then you are well on your way to nailing the perfect plank every time.