Ok, so actually there are no rules. My point is that once you start talking about mindfulness, you inevitably move away from the moment.
You may have the very best of intentions. After all, wouldn’t the world be a great place if only everyone did the whole mindfulness thing?*
Although you may want to tell the world about how great this thing is that you do, you should try really hard not to. As well as drifting away from the moment, you’re putting your own value judgements on to your practice. These judgements come from your past experiences and your expectations of the future. These things are very definitely outside the present moment.
So try not to do it.
*maybe; maybe not.