"The rules" are actually, what you, as a sub/master want them to be. Really, the best advice is to sit down with your partner and negotiate the terms of your relationship. And this goes beyond merely the use of a safeword when doing a scene.

Points to ponder:
1. A D/S relationship is a *power sharing* relationship. Really. It is said that the sub in the relationship has "all" the power, because s/he has the ultimate power: to end it, by walking out. This is crap. Yes, it is the ultimate power (as in "final"), but ultimate is not "all", by any stretch of the imagination.

2. How far does the D/S relationship go? ie, is it just in the bedroom, is it in domestic situations, does it cover any aspects of the sub/doms life outside the relationship?

3. Is the relationship to include others outside the relationship at the direction of the dom? If so, what activities are permitted, how often, and under what overall conditions?

4. Is switching roles to be allowed? If so, again, how often/under what circumstances?

5. Whatever the agreement, RESPECT it. If one of you feels uncomfortable with doing certain stuff, state that. And remember, it is possible to negotiate further negotiations. People are often curious about something, try it, and find they either do or do not like it. People do change their views. A regular "contract review" session (weekly, monthly, whatever you're comfortable with) should always be part of the plan.

6. Approach all this not as a burdonsome job, but as a fun activity. Hey, agreements can in and of themselves, make for some good foreplay.

7. Have fun, whatever you do.

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On the kinkometer, my kink measures as a sine wave.