So I'm going to demonstrate how to do a prone plank.
So basically, what that is, is a normal plank. If you hear people talking about planks, it's usually just a plank on your forearms with your hips lifted. You're kind of like in a surfboard position, on your forearms, you can also be on your hands. I'm going to show you first, on your forearms, what that looks like. Elbows are going to be right under your shoulders. You can put your hands flat, like so. You just want to make sure that your pelvis is tucked under, and your bellybutton is . . . I say squeeze your bellybutton into your spine as if somebody's about to punch you in the stomach. Think about me coming over, and giving you a nice little punch in the stomach. You're bracing, that's how you're bracing.
You can also do this on your hands, which is going to add in a little more shoulder. Again, your hands are right under your shoulders, you're lifting, pelvis tucked under, and your bellybutton is squeezing all the way to your spine. Try to relax your shoulder blades. You'll see a lot of people like this, wrong. Try to relax your shoulder blades and stay tucked under in your pelvis. So those are the basic ways to do a prone plank.