General Principles of Movement
It all starts from the ground up therefore it is essential that you learn how to root yourself to the ground. Your foot has mechanoreceptors that provide essential feedback to your body helping you perform at a higher level. This being said, it is important that when lifting you use either flat soled shoes like chuck taylors, olympic lifting shoes or bare feet. This will enhance your ability to feel the feedback and increase your performance.
Creating linkage is another key point and can only be optimized in accordance with rooting. We have to look at our body as it is, a collection of segments connected by joints. In order for our body to operate at its optimal levels we need to connect the segments through the joints forming linkage. Simply put, imagine a beam supporting a wall that has a kink in it, it will eventually fail to hold the wall up because the link will be compromised.
To effectively link we create tension, another key principle. We do this through muscular contraction therefore never locking out the joints but instead optimizing our muscles ability to perform through enhanced output of our muscles ability to fire through tension and thus linking our segments. In Crossfit we are not training bodybuilding, we are training athletics and in athletics we use our whole body to perform, not individual segments.
The core is key for creating the linkage of the upper and lower body. Also, it is key to protecting the spine and maintaining midline stability and a neutral spine. This is done by inhaling in through the nose through the diaphram and deep into the belly (think belly button) thus creating a strong core. A good way thing to imagine is pushing your core against a belt as your breathe. This air will add volume to your core much like sticking a pencil in mud making your spine stabile.