There is one aspect that by now I have realized as particularly important for a D/s relationship: The recognition feedback loop - at least that's how I like to call it.
What I mean by that is a (strong) need for the submissive part to gain recognition by the dominant part. The [knowing] dominant part ensures that such need is satisfied by
- making sure the submissive knows what kind of behavior is valued by the dominant, and
- actually granting that recognition if the submissive part actually behaves accordingly
I believe especially the latter part is important. The submissive part might feel insecure about what she (forgive my ignorance, I am always thinking in maledom/femsub terms) does, and whether it is really the right thing to do. So if she doesn't get encouragement by recognition, she might try something else or simply give up at some point.
The 'feedback loop' (technically speaking probably rather a feed-forward loop) probably gets into place if the desire for recognition becomes a need for recognition, and is strong enough for the submissive to go very far in order to obtain that very recognition.
So initially, maybe much simpler things (actions/behavior, whatever is desirable) result in the desired amount/level of recognition, but over time those things become much more normal for both sides, and thus sub needs to do more or other desirable things in order to gain the same amount of recognition than before.
There is a lot of difference in how much recognition a person needs. Some people base a lot of their self-esteem on the amount of recognition they get from other people (maybe even only close people). Obviously for this kind of person, the mechanics as outlined above should work even better.