1) At least half of the music in the session needs to be stuff that you're interested in playing; at least half of the rest needs to be music you're interested in listening to.
2) A strong rhythm section is more important than strong tune players.
3) No one should ever hog the floor without the absolute consent of the room.
4) Non-musicians in the pub should never make life difficult for musicians. Musicians in the pub should never make life difficult for non-musicians.
5) Space should be left for surprising things to happen.
6) There should be enough musicians playing to cover up your mistakes, but not so many as to disguise your successes.
7) There should be enough room see every other musician directly, to sit down if you want, and to get to and from the bar with ease.
8) Hostility to musicians with different tastes to you is always a bad look. Never assume that a choice is made out of ignorance.
9) It is always better when the spectators are dancing.
10) There should come a point when the room clicks into focus. The point of focus won't come quickly, and will disappear shortly after it arrives. Perhaps a tune will be thundering off with unshackled heroism, perhaps it will have locked itself into a taut and bodily groove, perhaps the room will be brittle with a sort of quietly numinous tension. But there should be the sense from the musicians that they aren't just creating the sound, but riding it - that they are losing themselves in something much older and stranger and bigger than they are. And every preceding moment will have been worth it for this.