Jwoo – basically the people always move between different colored areas (never from green to green etc).
And your buses must provide them faster travel route than walking (wait time + travel time). So you dont need too many stops (there is no coverage like in other games. you dont need too many stations to cover better area). You should make the lines so transport between different areas is as fast as possible (so dont let your bus go through 12 stops in green areas just to pick as many people as possible). And you should consider adding more vehicles on the line. Bigger frequency = shorter waiting times = more customers.
It is quite realistic system really. Your lines will only make money if they actually help people. Not if they are in populated areas like it is in another games.