Before the lights, the camera, the action, there is the unsung hero of any great video endeavor: pre-production. Sure, being on set has its own allure; and yeah, post-production is where the story really comes together. But without the thoughtful, meticulous work done in pre-production none of that would even be possible. In short, pre-production is where you build a solid, reliable base that sets your video up for success.
At the risk of being reductive, pre-production is all about two things: top level creative and logistics.
On the creative side, pre-production is all about fine tuning your concept, writing a polished script, storyboarding, etc. Really just doing anything and everything possible to ensure you have a firm grasp on the story you want to weave.