‘Windowing’ begins before the train even arrives. Evaluate the platform. Look for the least dense concentration of people. Is the top end of the platform quietest? People tend to amass in the middle, but don’t take that for granted. But simply looking for groups isn’t enough. Are you at an outdoor platform? What’s the weather like? If it’s cold, people might be waiting inside the ticket office by the radiators. They’ll pour out towards the nearest carriage, and the section of the platform you thought was quiet is now anything but. If you don’t beat them on they might take the seat that’s rightfully yours. This game is ruthless.
As the train arrives, evaluate again. Look for empty seats as the train slows. If others are likely to beat you on, consider cutting your losses and trying another carriage. Remember that people aren’t that observant, especially early in the morning. A clear belter of a seat may not be snapped up by the groggy commuter. Be prepared for anything. Read and react.