2) tap the glass bowl on a glass or otherwise clashing hard surface to try to clear the ash (use a pick to scrape)
3) handle your glassware in any other way that makes the old hats cringe
4) fail to hold the carb shut while drawing the pipe, and/or leave uncleared smoke in the chamber
5) fail to pull out the slide/pull/bowl after drawing from a water pipe (aside from leaving the chamber uncleared) this makes air kickback from water pushing back up tt the bowl, spilling smoke/plant material/ash/active embers up out of the bowl
6) He who blows into the water pipe sucks the water out of the carpet. e_e
7) A decently small amount of tar/resin does get you incredibly stoned and many save and salvage it later when in need (ask before cleaning/throwing away (protip: filter/scrape/dry pipe-water and smoke it again @_@)
8) The stems you pick out of the bag also have active chemicals that work if you filter the harsh smoke, but in a group set them aside when breaking up the material to pack (some like to save these for cooking as well) don't put seeds in.
9) If you don't know or you fuck up, say something. The more we pay attention (in life), more goes around, less is wasted, and we and our equipment are safer.
10) Also remember each group probably has their own tweaks. Just be respectful.