Somewhat like a submissive, a Dominant is likely to enter this lifestyle as a sadist, or with ideas of finding an immediate-type submissive, possibly for kinky-sex.
As the one who challenges the senses of the submissive one of the first things that he must learn is how to challenge and how do it safely. The early stages here are purely mechanical ~ involving tying knots, and learning how to wield a whip, flogger,and crop and the use of a candle.
If their relationship is more one of role playing and fantasy scenes, then he must also learn how to create scenes in his mind and how to express them to his submissive in a story teller fashion.
His growth might end at this point. He might remain an immediate dominant.
Further development requires that he don a mantle of significant responsibility because to involve himself with a psychological submissive or a slave means exploring and playing with the sensitive emotional and spiritual sides of his submissive. Cuts and bruises caused by a whip or flogger will heal in a few days, but the real emotional hurt that a dominant can inflict on a trusting submissive by poorly chosen words or actions can take weeks or months to heal, if ever.
The skills required by this type of dominant include perceptiveness, compassion, wisdom, sensibility, understanding, empathy, patience, openness, honesty, the ability to communicate, the ability to explore trust and the ability to explore intimacy, both his submissive's and his own, without fear or deception.
Some dominants have these skills. Some must learn them. Some will never have them.
The dominant of a psychological submissive or a slave will take often the role of teacher and mentor for his submissive. She will look to him for guidance and authority in her exploration of herself and where she fits in the lifestyle. He will need to be sensitive to her changing needs both within scenes and in "real-life" as her submissive aspects develop and integrate with the rest of her personality.
Of course, the dominant must learn these things, often doing so with a submissive whose experience reasonably matches his own, growing with her and, undoubtedly, making mistakes along the way.
The best tool that the dominant has to aid his learning and his growth is his ability to communicate with his submissive. By talking with her, discussing her reaction to him and to their scenes together he will learn how she reacts and gain more confidence in himself. From her and his growing pool of experience he will develop new ideas and new approaches.
He needs to be very open and very accepting. It will often be the case that his own preconceived ideas will be clearly and definitively wrong, and he must be ready to read the signs and hear the words from his submissive that tell him so. Stubborness in some things is good, but responding and adapting too slowly to his submissive can be just as damaging to the submissive's trust as responding badly or not responding at all.