You won't believe how much stronger this will make you. Since power comes from the ground up, learning to push your feet into the floor with all forms of pressing will increase stability and overall power.
There are two ways to do this: with your feet out in front of you, or tucked below your knees.
Both work, and the key with each is to think about driving the heels down into the ground.
Given the desk posture adopted by many, the chest up cue will help correct shoulder position and place the back in the correct alignment.
For example, when incline dumbbell pressing, thinking about lifting the chest up to the ceiling will create a slight arch in your back and pull the shoulders back where you want them.