Article originally found in sc4ever.com
If your trains don't appear when you place them, then you must be doing something wrong, right? Wrong. You just placed the stations in the wrong areas. See Simcity 4 is very realistic in the sense that if you don't place your passenger train stations where it's crowded, then you wont be receiving any people riding your trains. The same with freight, place them in the heart of your industrial...then you are sure to receive freight trains.
If you don't know where the traffic is, just go to the traffic meter and it will show you, place stations only where the roads are deep red. But not too deep into residential, cause not even you would want a train riding past you while your sleeping right?