In order to get to top 10 list I use phantom line tactic, otherwise its impossible to get those high scores. I was getting around 1500 score without using this tactic and I'm getting close to 3000 when I use it. But this ruins the fun of the game because I need to use it constantly and it's boring.
Phantom line tactic : keep one or two lines and trains unused. Use them momentarily to clean overcrowded stations. Create a line from an overcrowded station to another station where most of the passengers in overcrowded station wants to go. The moment train leaves the first station you can remove the line and use it in another overcrowded station if you have another unused train.
What I suggest is to have a new game mode, called Hard (or something) that will be like normal but when a line is removed it will have a delay of 10-20 seconds to be available again in order to make this phantom line tactic unusable. This should be a new mod because if normal mode is changed, then current high scores will not be reached again.