I don't like much formality in jiu-jitsu, or even life in general. Politeness doesn't have to mean a set of arbitrary rules. That said, I do think there are some rules of etiquette worth following in jiu-jitsu...
1. Be clean!
This is the most important. There is no reason or excuse to have poor hygiene at any time, but definitely not when you're taking part in a sport with such close contact. This means...
- you HAVE to wash your gi every time you wear it, and do it as soon as you get home... don't leave it sitting in your bag for hours.
- wash your belt! I know people who say you shouldn't wash your belt for whatever stupid superstitious reason, but the simple fact is your belt can smell and contain bacteria just as much as your gi. It doesn't get as sweaty so doesn't necessarily need cleaning every session, but do it regularly and especially after any particularly sweaty sessions.
- you should be clean and not smell when you turn up for training. You don't need to shower directly before (and I've read that this is actually a bad idea as it makes you more susceptible to picking up infections) but you must be clean.
- your finger and toe nails should be short, nobody wants to roll with Wolverine.
- you definitely shouldn't train with anything contagious; skin conditions or general illness.
- if you have any cuts/open wounds make sure they are totally covered, and if the tape/bandage/plaster comes off throw it in a bin and replace it immediately. If you bleed on the mat, tell your instructor immediately.
2. Always remember you are a representative of your instructor and academy
When you're talking about your instructor or academy online, or you're waiting in the reception while the kids class clears out, whatever situation be mindful of what you say. Something which is an in-joke at the academy could sound very different to an outsider.
3. Treat your academy with respect
It's the place you go to train and probably spend a fair amount of time at, so don't leave your rubbish in or outside the academy and definitely don't step on the mats with shoes on!
4. Treat your instructor and training partners with respect
Should go without saying. Also, adults shouldn't need to have this explained to them; obvious things like you should listen to what your instructor says, don't talk while they're explaining technique, don't belittle training partners or make anyone feel uncomfortable etc...
5. When rolling and you are close to another pair, the lower grades should move... most of the time
I don't like imposing rules of seniority but in this case someone has to move and I think it's fair to let the higher grades get on with it. However, if one pair is just sitting in a closed guard and the others are halfway through a berimbolo, it's much easier for the pair in guard to move regardless of grade.
6. Don't talk about who you can tap or who you swept etc
For numerous reasons; firstly training is training, the only submissions which really count are in competition. Secondly, it breeds a poor training environment and takes away from a sense of being a unified team. You are meant to be there to help each other improve, not trying to beat each other and feel like you need to prove who is the best. Definitely never celebrate tapping someone in training!
7. Don't undermine instructors or students
If you feel an instructor has taught something incorrectly then speak to the head instructor not other students, definitely don't talk about it in front of the whole class. If you have an issue of any sort with another student then again, you should speak to your head instructor and not start talking to other students about it.
8. Respect the tap
When someone taps, you stop, end of story.
...and I think that's about it. I may have forgotten something though, and would be interested to hear anything you think should be added.