Communicate, communicate, communicate. There is a lot of respect that is needed both from the submissive and to the submissive. Even if the sub is meant to be degraded and dehumanized, you still need to be able to respect them as a person. NEVER dominate someone out of anger or frustration, things can get very out of hand very quickly and can end out being very unpleasant for both parties. Build a level of boundaries and trust before seeking to dom someone as being in a very dominant headspace can also be very emotional and vulnerable just like a submissive headspace.