There should be a Dominant. Since he (assuming it is a man that is the dominant, not always true) has the power, he also has the responsibility to the submissive. That includes giving her pleasure, knowing and doing what makes her happy, prodding her to be her best, helping her reach HER goals and dreams, etc . He does not try to shape her in his own preconceived image of what she should be, but instead helps her blossom into the complete and wonderful person that she is. He knows what is her best, what she wants, what is best for her because they have a totally open relationship in communication. The Dom should respect the Sub's advice and point of view, but the decision is his. This assumes the Dom makes decisions not based on ego or emotions, but logically figures out what is the best decision. If the Dom does something that hurts the Sub, she should be able to tell him in an informative manner, not an attacking manner. The Dom will also tell the Sub how he feels about her actions in an non attacking manner. As I have often said, for the relationship to work, both sides must respect the other to not attack and also to trust enough not to assume an attack. That right there, which is a form of a break down in communication, is what causes the most problems in relationships. The Dom should be secure and strong enough to admit when he makes mistake. Doms are not gods, they will make mistake, but once again if the basic assumption is that there is respect and trust on both sides then the mistake will be an honest one. Doms control not by fear, but by building desire in the Sub to obey. Essentially, Doms have the power and they use it to make the life of the sub more complete, happy, not to abuse them.
In reality the way it works is that the Dom acts more as a discussion leader then an arbitrary decision maker. By leading the sub through a balanced discussion, including parts of the issue that the sub may be unwilling to face, then the sub can make the right decision for herself. Usually the Dom, because he knows his sub so well (due to the open and honest relationship and the intense intimacy that it brings) , can often see things that the sub cannot or will not admit. Once the sub makes the decision, the Dom supports her, and possibly helps her stay "motivated" (many wonderful ways of doing that :) in implementing the decision.
The Submissive should obey her Dom, and strive to please him, for essentially for one reason; because that is what makes her happy (that assumes she trusts and respects him). Notice what I said should be among the things that should please the Dom, prodding her to be her best, helping her to reach HER goals and dreams. Thus, she is motivated to do what she should do by TWO reasons now, first it is what she wants to do, and because it will please her Dom. Because there is open communication (something I demand), if the sub has a problem either what her Dom says or anything else she tells him, she should feel free in telling the Dom her opinion and thoughts, but trust in him to make the fair decision.
Most subs start out with what could be called split personalities, a somewhat Dominant, commanding persona, and a submissive, little girl persona which she hides. A good Dom first builds the environment where the submissive can let out the hidden persona and feel safe doing so. It enables the sub to explore her self and her desires and fantasies. Because the Dom accepts ALL of the sub, including the hidden persona (actually if they are like me are attracted to that persona), she should gain strength in her hidden persona, not look at it as a flaw or weakness. This is the key to the D/s relationship, and that is acceptance. In a battle of wills, you do not accept, you fight to win. If someone exposes a weakness, you exploit it for victory. Thus, both partners feel insecure because they have a "secret" persona that one hides and feels threatened by.
The key to all of this, as it is in any relationship, is communication both ways. The openness in a D/s relationship is what is missing in most marriages. For one thing, openness, by constantly expressing your thoughts and feelings in a non attacking manner to a partner who is concerned with them, builds intimacy of the mind. Mental intimacy is much more powerful in bonding then physical intimacy. That is why cyber/long distance relationships can be so intense and go so fast, because all you do is communicate, with occassional physical meetings. Mental intimacy also leads to Mind Sex. Mind Sex is the ability to make your partner orgasm with NO physical contact by anyone, including masturbation. Just your mind, her mind and his voice. It creates a new level of intimacy. Unfortunately in most marriages, because there is a battle of wills, one does not want to open up completely for fear of giving something that the other side can use against you. Thus as the battle continues, communication and openness drops, and so does the intimacy of the mind if it really ever existed.
People often confuse a D/s relationship with a Controlling one. My former in-laws have that. The man is a controller, where he controls just to have control and is not concerned really at all with his partner's welfare. Generally the controller is so insecure that they have to demonstrate their control over everything, thus they control by using fear.(A Dom builds desire to obey, not fear) The woman meekly obeys out of fear (no physical abuse but some emotional abuse) and "for the good of the kids" even though now the kids have gone. Her spirit has been broken and she survives by doing things behind his back. Her children have told her to leave him, but that is not the way of her generation. Many think this is what is meant by being submissive. It is not. It is being weak, for she constantly gives and never gets back. I personally think in a true complete relationship, both sides get back much more then they put in, for why be in the relationship if you do not benefit from it.
Bottom line, the D/s relationship is a circle where both sides concentrate on meeting the needs and desires of the other from their different roles. If one gets pleasure out of pleasing a partner, and that is true of both sides, then the relationship is built on one will, not two and the conflicts (assuming as always, that you have picked the right partner) will be minimal. The relationship will provide you the benefit of having someone you can be TRULY (mentally) intimate with, and gain strength that comes from exposing your perceived weaknesses and having your weaknesses nurtured and cared for and turned into strengths. It is not about control it is about communication and mental intimacy.