In reading various threads and chatting with other submissives, one particular thing becomes clear to me - how important consistency is in a D/s relationship. It is a vital element of so much of what we do, and one that can wreck a budding relationship in an instant.
Communication - consistent communication. In two ways - first, show up when you say you're going to! This goes for both Dom and sub. Second, the practice of leaving a submissive hanging, waiting to hear from you, for days or weeks, simply because you can, is just wrong. It's very damaging. I can't count how many submissives I've talked to who have had this happen to them. If you're truly unable to spend time with them because of other issues, drop an email, telling them that and when you think you may have free time again. It makes a big difference, believe me.
Constraints - be consistent in what you do and don't want your submissive to do/be/say. We love the excitement of change, but don't set us up to fail by changing what we can do or say when our brains are barely functional. We hate, hate, hate failing. Hate, hate, hate not doing the correct thing, every time. Hate, hate, hate disappointing you. So if you want a radical change in how we interact with you - tell us when we're coherent, ahead of time. Please?
Commitment - be open and honest and consistent about your level of commitment. If you do not want a daily interaction with a submissive, say so! On the other side, if you expect any sub of yours to devote 6 hours of her day to you, say so! And please...no "I love you" one day and "Who are you, again?" the next. That can be crushing to a submissive, even more so than in a vanilla relationship I think.