Never be in a training room with a dirty/stained/unkempt uniform and *always* have your belt on - unless you have just passed a belt test and are waiting to be presented with your new one. A belt is never removed in the training or public area.
No talking amongst each other either in the training room or in the waiting room. Something I ran into when visiting another school recently, parents who yell out to their children during a children's class! "Billy, the other way! pay attention! step over!" 
Never, never, ever....
Just wanted to point out that a these rules can differ from one dojo/dojang to another; the important thing is to respect the rules of the school you are in. When in doubt, of course default to the most respectful conduct you know.
My school for instance tended to be somewhat informal; full uniforms were not required to participate in class, and putting on/removing belts in the training room was acceptable (this room was larger than our actual training area). More importantly, talking among ourselves was not only allowed but encouraged. We were a club created for the enjoyment and training of like-minded students--it was pretty much expected that we would chat while warming up, joke with and encourage each other while training, give advice to others having trouble, etc. When the instructor spoke or a higher-ranked student gave instructions, everyone listened, but otherwise we were free to talk, as long as it didn't interfere with the class.
oh, of course it's different between schools (and styles)! 
That's why I put what styles I had experience in at the beginning of my post, to point out those were the rules in the courses of MY training experience. I know schools differ in formality levels. After visiting other schools and knowing people from other styles/schools, it came to my realization that my school was almost militant in its formality 
ETA: My last statement in my post, though, I still can't believe would be acceptable in any school: the yelling out of parents in the waiting room to their children in the training room, during a class being taught by an instructor. Maybe it's just me?
Oh, I definitely that the parents shouldn't be interfering unless the instructor has specifically asked (My school was a college club, so the only kids we had were a couple of children of a professor; they were quite mature young ladies, so there was no reason for their parents to yell to them.
)
What I was responding to was the "No talking amongst each other either in the training room or in the waiting room," which was in the same paragraph. I just wanted to point out that that wasn't a "standard" rule for martial arts classes that I knew of, especially not for adult classes. I realize you were describing the style in your school; I just wanted to make sure it wasn't taken as "standard dojo etiquette" by someone less experienced, since it would vary widely depending on school or just even on who's teaching that day within the same school.
BTW, a question: when discussing general martial arts (rather than a specific type, such as Karate, Tae Kwon Do, etc.), how do you generally refer to things like a martial arts school, a uniform, an instructor, etc? Do you use the terms from your own style, more generally know terms (e.g. the Japanese terms used in Karate), the equivalents in English/whatever language you're speaking? To clarify, I'm learning Tae Kwon Do (a Korean art), so the school and uniform would be called "dojang" and "dobok", respectively. But "dojo" and "gi" seem to be better-known terms to the general public. So in my position, in a thread like this about multiple arts, would you use the terms "dojang" and "dobok", "dojo" and "gi", "school" and "uniform", or something different?
