Owning a slave is no small thing. Even in the setting of a game, it is still no small thing. We have a tendency to invest ourselves into our favored characters and derive some considerable pleasure and satisfaction from the relationships that those characters involve themselves in.
It can be a daunting prospect, but that should not dissuade you from taking the challenge. There are, however, a few things you should consider.
1) Communication, communication, communication. Nothing is more important than this. Nothing. Some aspects of the relationship can be embarassing and even frightening to those unused to the idea. Sexual aspects, control aspects, boundaries and allowances, all of these things 'need' to be established beforehand OOCly, even if you intend to flesh them out ICly. You cannot expect the mun behind the slave char to just 'know' what is expected of him/her. And you cannot allow yourself to get angry or upset when the slave's mun comes to you with something you may not want to hear. It's unfair to you both to give the impression that you're not willing to listen to him/her.
2) OOC/IC separation. Your character owns another character, but this should never translate into the OOC. You don't own the character's mun and you should never assume as much as to try to treat the mun as if you do. This means you can't make assumptions, demands, expectations or boundaries on that mun. You can't tell them who they can or can't play with. Emotions are impossible to avoid, but you can't allow those emotions to force you into bad actions.
3) Know Thyself. This means mostly knowing just why you're accepting the challenge of playing out that owning of another. What exactly are you hoping to learn? What aspects of the Roleplay do you enjoy? Knowing what 'you' want out of it is as important as knowing what the slave's mun wants out of it.
4) One Size Does Not Fit All. Every slave char is different, every Master char is different. Don't expect your behaviors to invoke the same response in every slave char you run across. It just doesn't work that way. Expect to learn new things every time you take up that challenge, expect to be challenged to adapt and grow.
5) Change or Die. To many, the chase and then capture of the slave char is the whole of the challenge and the captured slave char is to be enjoyed fully from then on. However, that is really shortchanging the slave char. Yes, a collar is often the culmination of much Rp between the two chars, but is not the end of the challenge. It is wise to consider further challenges for the slave char, either by ICly placing goals for the slave char or forcing him/her to adapt to IC demands. This is something that should be explored deeply on an OOC level so that there is no confusion.
6) Have fun. This is the golden rule of 'all' RP and the only one that should be kept in mind at all times. If it ever gets to the point where it's no longer fun, then some serious conversation needs to be had.
~I~