- Have your ticket/oyster/card ready BEFORE getting to the gates (and move to the side and out of the way if you need to take time to find it)
- Move inside the carriages
- Don't start conversations with commuters (especially during morning rush hour)
- Take your rucksack off and put it by your feet if it's crowded
- Don't walk 3+ abreast
- Don't run for the train and especially don't block the closing door (there's a train every 2-3 minutes, just wait)
Other annoyances;
When you get to the bottom of the escalators don't just stop in the middle looking at phones and wondering what platform you need. Stand to the side.
Observe the queues next to each door position on the platform and join them. Do not just stand in the clear space in the middle. Following on from that, let people off the train first!!
Walk down the platform don't huddle at the entrance to it.
Don't wait for the gates to close before tapping your card. Just tap and check for green light.
This surprised me when visiting the UK.
I actually expected people to stand on the "left" of the scalators - just like how they drive on the left and overtake on the right - but they didn't. They stood on the right.
I was left puzzled ???
Cars stop on the left, which allow other cars to overtake them on the right.
DO ask people for directions or for help, people may look tired, they may look grumpy they may even be those things, but most will be more than willing to help you.
EDIT: Others covered a few important ones I missed too; backpacks off, walking N-abreast so as to be blocking others from passing are a big no-no; you may be having a leisurely stroll, commuters have places to be, whether at work or at home with their families and their feet up after a long day.
edit: Rule to add - don't just stand still when you step off an escalator.
Of course, these are all rules that should be followed by everyone on all public transport. Nothing really specific to the tube.