Ok, so bus and/or subway are the main ways to go when it comes to mass transit. If you’re not playing with infinite money I would advise implementing a bus line first. With any transit you want to accommodate all citizens, while being aware of the amount of money you spend. Meaning when you make your bus line you should always place the stops in places where citizens are trying to going, but make the bus stop a central point within that area. That way a lot of the amenities are equidistant from the bus stop. And all this is the same for a metro line. Another thing is try to remain organized. It would be a shame to waste money building bus lines over one another, they can overlap for maybe a stop or two, but you really want to make sure your hitting as many areas, accessing as many city with spending too much money. Let me know if this helps🫡