These are the three tenets of a D/s relationship. I have been asked to write this essay explaining these words and thier importance to a true D/s relationship. 

   First comes safety. This one is exactly what it states. Play safe. The best ways I have found to "play safe" are as follows. Open and honest communication prior to any sort of play helps to establish limits and a basis for trust. Discuss your needs, and those of your partner. Don't hide behind shame or fear of your needs. Be honest, this makes safety easier to maintain. Also, choose a safe word. One that does not normally belong in a scene. I have seen the words Red (stop) and yellow (slow down) used most often. Discuss what a safe word means to you, choosing one that is easy to remember. Make sure that the expectations surrounding it's use are discussed. Medical histories should be discusssed, with all avenues of safety from disease being used. To help ensure physical safety maintain your equipment in good condition. Be sure you know how to use it before you try anything new. Realize that rushing into things can cause physical harm, so take your time. A few basics, never play while intoxicated in any manner.

   Sane, well this one is tough. Who is to say what is sane and what is not? Each relationship is different. I must say that sanity as far as it affects D/s means, do not place extreme expectations on yourself or your partner. Be aware of thier emotional needs. One should never lose thier identity to another. Many of the things you read in novels are fantasy. A lot of it does not apply very well to the real world. Keep that in mind. Think logically before acting, make sure that what you are doing is actually possible before attempting it. Remember, D/s is a lifestyle but not one meant to take over your entire life. Stay within reasonable limits.

   Consensual means agreed to. The activities of D/s play should be pleasurable for both parties and agreed upon by both. This brings into play consent. Nothing should ever be done unless both parties consent to it. How much pleasure is an activity if you are forced to do it? I don't mean the gentle urging of your Dom either..I mean actual force. A Dom should never forget that he is the Dom only because the submissive allows him to be.
Without the submissive allowing such control, there are no Doms. Submission is a gift, rare indeed, and should be treated as such.

If the first two tenets of D/s are met as the relationship begins, then the third will come automatically. And the more the trust within the relationship grows, the more mutual pleasure abounds. SO play safe, exercise reasonable limits, and have lots of pleasure together.