"From here it was said: Whoever acquires a Hebrew slave is as if they acquired a master for themselves." (Kiddushin 20a) "From here" is the verse in the Bible "And it shall be, if he say unto you: 'I will not go out from you'; because he loves you and your house, because he fares well with you" (Devarim 15:16) describing the desire of a slave to remain such even after his period of slavery was over.
Based on the phrase "with you" our Sages derive that the slave must be treated as a member of the household. "With you in food with you in drink, you shall not eat fresh bread and he eat black bread, you drink old wine and he drinks new wine, you sleep on bed of feathers and he sleeps on beds of straw."
Giving one's slave wine is not good enough unless the wine is good enough for the master too. As behavioural economists have noted we tend to view our wealth in relative terms. For better or worse (mainly worse) we determine our wealth based on how we compare to others. And the "other" who a slave compares himself to is not other slaves but his master. The Torah demands we not only treat a slave well but we treat them as well as ourselves. Or even better than ourselves.
Tosafot, quoting the Jerusalem Talmud, explains if there is only one pillow the master cannot use it himself as such would be a violation of the Biblical command "because it is good for him with you" which mandates the servant be treated equal to the master. The master is left with no choice but to give the pillow to the servant. To have no one use it would be in the words of the Tosafists "the measure of Sedom." Sodomic activity is defined as refusing to benefit another at no cost to oneself. Sadly we see such an approach far too often where people are wont to say 'if I can't have it myself no one is going to get it either'.
Not only must a "master" treat his "slave" as an equal, or better, he must do so for the entire family of his newly-acquired slave. "And he shall leave you he and his children with him'; if he [needs to be] sold into slavery are his sons and daughters also to be sold to slavery? From here [we learn] that his master is obligated to support his children."(Kiddushin 22a) This teaching is followed by a similar one mandating that the master must also support the slave's wife.
When we recall why one becomes a slave these attitudes become even more remarkable. One was either "sold" by the court into slavery so that he (and it was only a he who could be sold by the courts) may repay what he had stolen or, sadly, a person could also sell themselves into slavery as a means of escaping poverty. By doing so the slave would have his basic needs taken care of. No wonder the slave had little interest in leaving!
Despite this mandate to treat a slave as an equal our tradition has a most negative view of the institution of slavery. "'For the children of Israel are servants to Me' (Vayikra 25:55) - they are slaves to Me and not slaves to My slaves." (Kiddushin 22b) Man is meant to be free and not indentured to others. The Torah is unwavering in its message that a slave be treated with the utmost dignity that all who are created in the image of G-d deserve. In a most remarkable statement the Torah commands that a slave is not to "do the work of a slave" (Vayikra 25:39) and the idea that a slave cannot work on Shabbat is included in the aseret hadibrot.
More fundamentally it was hoped that a slave would be redeemed before the end of his servitude - and if that did not happen he would automatically go free after six years - or sooner if there were to be a jubilee year.
While the institution of slavery no longer exists our Sages understood that almost by definition every employee is to some extent a slave. The Torah itself equates an employee and a slave (Devarim 15:18) - insisting a slave be treated no worse than an employee yet at the same time acknowledging that an employee is part slave. And while a slave could not just quit our Sages maintained that a worker be allowed to quit at any time so that his working becomes voluntary. To do otherwise would effectively turn an employee into a slave.
While the Torah legislates about enslaving others we must also ensure that we do not enslave ourselves to our own work.
 See here for a fascinating "cartoon" explaining the Torah's allowance of a father to sell his minor daughter to slavery.
 This would not be the only institution allowed by the Torah despite it being far from ideal. As we read sefer Vayikra I imagine most reading this are aware of the view of Maimonides that sacrifices were far from the ideal way of worshiping G-d.
 Employers must be careful lest they violate the prohibition of asking their employees to perform "slave labor". Such might be violated in giving employees "busy-work" the primary purpose of which is to ensure employees be kept busy. For a fuller treatment of this issue see Rabbi Dr. Aaron Levine, The Mean Boss, Case Studies in Jewish Business Ethics (pp.237-248)
 How this might - or might not apply - to the modern day workplace is a most important topic beyond the scope of this devar torah. Suffice it to say that one must be very careful not to create a chilul Hashem. Jewish law takes a signed contract very seriously. And to ensure one not sell themselves into slavery many rabbinic authorities forbade one to sign a contract longer than six years. And that might even include David Price's seven-year $217,000,000 contract (if not for the fact that he has an opt-out clause).