For years in traditional riding lessons, I heard things such as:
Sit up
Heels Down
Look up
Deep in the saddle
Hands up
Not until much later in my riding career did I start to realize that ALL of the rider's movement is connected. If there is not a strong foundation- starting with the seat- the rest of the rider's body will have unwanted "side effects" or excessive movement as a way to unintentionally compensate for a lack of balance and stability.