Don’t call it underground or subway. Londoners call their underground network as the ‘tube’. And as they say, “when in Rome, do as the Romans do!”
Don’t talk to strangers. Londoners never make small talk with one another on the tube. This is not just a safety trip (lest you end up having a conversation with a ‘mugger’), but also a custom of sorts.
When using the escalator to travel up or down, make sure you stand on the right side. There are signs stating the same rule everywhere. Be aware, not following this rule may end you up in a push and shove competition by a hurrying commuter!
Follow the queues and don’t try to push your way to the front. Yes, you may be in a hurry and but so are others!
Do not stand in front of the entrance/exit, automatic gate, in the way of an escalator (top or bottom) or the maps that are place for the convenience of commuters.
If you don’t want to look like a tourist in the sea of Londoners, memorize your routes. Take your time and look at the map once, instead of taking it out at each of your destinations.