As wildly politically incorrect as this is I've been musing lately about the best way to handle slaves.
With a tip of the hat to Jonathan Swift:
Obviously you'd want the most return for the least cost. Common capitalist business practice. Slaves being (unfortunately) human you must house, clothe and feed them at the least cost. But if you cut costs too much they might get sick and die and there goes your investment.
You need to understand that to the slave, slavery might be considered less than ideal as a system so you need to consider their social and cultural circumstances so as to keep the right balance of obeisance and will to work.
Anything which strengthens their bonds and identification as family and friends must be weakened so that their primary relationship is to you their boss. The less they see themselves and others as people and more as cogs in a machine the better for the bottom line.
However, there is a bright light at the end of the tunnel for you slaveholders and that is technology in the form of artificial intelligence, robotics and super computers. In the transition period to full technocratic implementation you will still need some slaves but considerably fewer than before and the numbers needed will sharply decline with the decades.
That leaves one final problem, excess slaves. Think carefully here. You can't just turn them out as they may turn on you and they will have large numbers. Mass murder although a viable choice with modern weapons, has its own very, pardon the pun, sticky problems. No, you must find a simple but effective way to reduce their numbers without at the same time creating more problems than it solves.