In reality I don’t use trains asap (I might have misinterpreted you, I thought it was a general comment).
I usually start with cargo truck routes and some intercity and intracity bus routes to get a solid financial base and spur some city growth.
After a while (typically 10-20 years) I replace intercity busses with trains. I usually connect three or four cities on a straight line based on population, distance and terrain (I often start with two but then extend the line asap and more with faster trains). I try to place stations close to the residential area, but I immediately set up intra-city busses to the other areas (often so that residential is in the middle of the route like industrial <-> residential <-> commerce <-> leisure). I often use 6 passengers wagons or more with the newer locomotives. For the first 2-3 years the train are at a loss, but then they begin to make a profit.
I still am not sure if bus lines would be even more profitable… but hey I like to play with trains 😉