As others have said, it’s situational. As an example, for Assassination, it’s more energy efficient to Eviscerate at 6cp vs Mutilate for the 1 extra cp. Learning when to clip or not clip cp’s comes with experience.
Don’t spam keys. This will cause you to unnecessarily burn through your energy. Worst thing you can do as a rogue. Practice getting into a rhythm and pace yourself. Learn when to pool energy and when to let it all out.