Some suggestions for whitebelts...
Don't strut around in a brand-new Lucky gi when you haven't been training over 3 months.
Don't announce that you're doing jiu jitsu because you keep getting jumped by at least 3, up to 6 people. It makes you sound like you ask for it on a regular basis even if you don't.
Don't try to submit people from inside their guard. Yes, even if it's a girl who weighs 60 lbs less than you. Even if it's physically possible for you to get her arm into position for an americana. Even if she's nice by not armbarring you first and explaining later-- she's not lying to you when she tells you someone else won't hold back.
Don't nod and say okay when offered advice by a higher belt, then proceed to ignore it and shamelessly do the same thing again. [Note: not talking about repeating mistakes out of inattention or ignorance; that's understandable.] Then, when you're being armbarred as a result, don't pick them up and drop them onto the mat on the back of their neck as you strip your arm free. It might hurt them.
Don't grab onto submissions and yank them. When your opponent is talking you through how to execute the technique correctly, they're trying to help you, so it's a good idea to listen, because it means the "competitive" part of your rolling is temporarily paused so they can actually be on "your side" for a minute. If they say something like "whoa, slow down, be gentle" that means you're going too fast or grabbing and yanking. If you continue to do that, you will end up hurting someone and no one will be happy to roll with you. Or, you might get pwned by some higher belts for a while till you learn manners and control.
Don't play rude jiu jitsu when you're just training; save it for a tournament if you absolutely insist. Example: when you're doing knee on belly, it's okay for training to put your knee across their hips instead of hunting around for the solar plexus, especially if your opponent weighs 60 lbs less than you do. Especially if you also have collar and knee grips and are bowing them up into you. And, if they ask you how much you weigh, it might be a hint to move on from the position, or take a little weight off.
Don't ignore it when training partners tell you up front about injuries they're training with.
Don't reach back with one hand to break open guard. Don't complain about getting triangled when you do.
Don't go a million miles an hour or use every possible opportunity to explode out of positions.
When you have someone on your back with hooks in and one on one grips on both your arms, don't do a fast forward roll when you're closer than 4' to a wall. While bashing your opponent into the wall will probably get them off your back, it might be bad for their face and neck.
Yes, this was my lunch open mat. All in about 10 minutes.