Well, first off, I kinda guess the term "rules" raises some questions for me. If the other person/people involved are adults and if you are not in some knd of paid and/or contractual supervisory position over them, then, really, you just do not have the right to make rules for other adults..and it is disrespectful of their human dignity and of their right to make their own choices -- however unhealthy and self-destructive those might be -- for you to try to do so. (I'm just bringing this up because I think the language we choose to use can tell a lot about where we are emotionally, and when you use the word "rules" in connection with your A -- who I'm assuming is your SO also -- it tends to cast your relationship in a parent/child light and, if you're feeling that kind of "parental" responsibility for your A, then that right there is a situation that is pretty unfair for both of you.)
Now, other posters have assumed that when you said "rules," you meant boundaries. Boundaires are another matter altogether. As others have said boundaries are about you and about what you are willing to put up with and what you're not going to put up with. You have the right to set them and the right -- and responsibility to yourself and to others -- to enforce them. If you set a boundary and do not enforce it, then you are, not only allowing yourself to be disrespected, but setting a situation up so that you can be and you are enabling disrespectful behavior in others. That is behavior that only makes everything worse for everyone involved.
So, here's the part that always used to get me stuck when it came to setting boundaries with my partner: I knew that I wanted to set the boundary and I knew that I could and would enforce it...but I also knew that, if I did so, it might lead to consequences that I really did not want, i.e. to her getting really angry and behaving even more poorly and maybe even leaving.....So, I use to spend lots and lots and lots and lots of time and energy thinking about exactly how I could do it/say it in such a way as to get the outcome I wanted (that outcome being her willing compliance so that we could live "happily ever after).
And, of course, the reason that took up so much time and energy was because, in reality, the outcome was not mine to control or to predict or to worry about or to plan around......What was mine to control was just doing what I needed to do based on how it was best for me to take care of myself at that time. In other words, just to say what I needed to say as simply, as directly, and as non-hurtfully as possible (This is not to say that the A might not choose be hurt, because, in my experience, an active A can find a way to get hurt by anything if it gives him/her an excuse to drink -- but you're not responsible for that either!)....and then to deal with her response -- whatever that was -- in the same here-and-now self-respectful and self-care based way when it happened....
.....and, yeah, at one point that ended up taking me somewhere (throwing her out) that I might never have gone if I had been stuck in fear and in controlling it all and plannig it all out in advance....but HP had other plans and, it just so turned out, that HP's plans were much better than mine ever could have been even if they had "worked out" perfectly...
So, no rules, only boundaries and enforcing boudaries one day at a time to take care of yourself, not to control anyone else or the future...Really, it's the only sane way.
freya