Stay on the right if you don’t want to walk up/down the escalator. If you want to walk, go to the left, but keep it moving. If you decide to stop on the left side, you will be swiftly told to move, which is often accompanied by a less-than-pleasant frown from the patron behind you.
If you don’t know what you’re doing, GET OUT OF THE WAY and ASK! The tubes are always overfilled with businessmen and women, students and locals who are all trying to get on the next tube towards their destination. They understand that you’re a tourist, but please don’t stop in the middle of the flow of traffic to look at a map. There are tons of phone apps that will give you seamless directions from point A to point B.