The blog 100 Improvements to the New York Subway has some suggestions I feel are relevant for Transport for London as well. Here’s one I liked that could be implemented on London Overground stations, as well as tube stations that are above ground.
49. Solar Panels on Outdoor Stations
The installation of solar panels on outdoor stations can help power the grid of the subway, and as an extra source of income, the MTA could sell earned energy back to the city.
See the rest of the entries to find other suggestions on how to improve the New York subway system, and possibly find some ideas on how to improve TfL, Bangkok Skytrain or whatever your urban transport links are in your city.