TL;DR - Be excellent to each other
This document extends the generally accepted social contract of being a human being and in particular one having lunch with strangers; be nice.
Dim Sum is traditionally a morning/lunchtime food so DimSumJS is intended to occur during your lunch break. This occasionally means people have to rush back to the office so if you arrive late, you may still be eating when the bill arrives.
Dim sum is a social meal so sharing food is absolutely encouraged. Be adventurous in your ordering, pass food around and try a little bit of everything on the table.
Tea is a central part of the dim sum experience. When pouring tea, grasp the teapot with your right hand and offer to others before filling your own cup, starting with the person on your left.
If receiving tea, thank the pourer by tapping your fingers on the table. Tradition says to use your index finger if single or index and middle fingers if married or if it's none of anyone's damn business.
When the teapot is empty, turn the lid upside down and/or leave it on the side of the pot, this signals to the waiting staff that it should be refilled.
Don't feel the need to wait until the end of the meal to order sweet dim sum. It's normal to order and eat 'dessert' dim sum alongside the savoury stuff.