What are your cardinal rules for hitting a baseball hard?

For me, they are :

Weight transfer (Not squishing the bug is my main indicator)

Hip Coil (I feel a little burn on my back hip after a couple swings)

Lower/Upper body separation (I feel a delay in my swing as if someone's holding in me back)

Staying short to the ball (The way I visualize it is that I must have a little bend in my left arm, while it might not work for others it works for me)

What are yours, And What should I also focus on?

I follow KISS

Keep it simple stupid