I just received my first macbook. It is my personal computer and I only use it in the evening as I am at work all day. My question is how can I achieve optimum battery life? Should I always use it attached to the charger (if possible)? Can I leave it attached to the charger after it is fully charged (like while I am at work). Should I turn off the computer during the day or just simply use the sleep mode? If I do use it off the charger should I let the battery run down or charge it even if it is at 75%. Thanks!