For any given clubhead speed, the easiest way is to improve "centered contact", i.e. the closer the angle of clubface is the path, the greater the energy transfer to the ball - goes along with centered contact on the face also.
TGM advances a theory that by maintaining "lag pressure" until separation, you minimize the "decceleration" caused by impact. According to this, a "good" swing will only lose 20% of club speed between impact and acceleration - a "poor" swing would lose much more. Ball speed is a factor of club speed at separation + the coefficient of restitution caused by impact. This theory is up for debate at the current time - although the "idea" of maintaining pressure helps many improve.
In simple terms, improve "compression"
Bruce