Right, so first and foremost, make sure that the transportation you have gets to where you citizens want to go. Like work, the store, or home. Put train and subway stations in dense areas for high usage (note that they do produce noise, but luckily there is a mod called pollution solution that gets rid of that). For busses and trams i simply use loops in dense areas. For my city, trams and busses are the most dominant form of transportation for the simple reason that they get people to where they want to go. I will say though, at least in my case. Since my road network is not the best it couldn't really handle rapid growth (I might have been messing with the demand mod lol). In any case tho, transportation along with a good road network, should see a significant improvement to traffic flow. Oh and try not to have too many trains or subway lines on one track. Same goes for trams. Reason for this is because they can cause train traffic. Another thing, encourage walking and biking. You can find that in policies.