Where to start our rail empire?
We can not start a service between 2 points too far away from each other. After building tracks and stations there isn't enough money left for an engine and some carriages/wagons. If you do spend all your money this way and take out the maximum loan at the start be prepared to go bankrupt!
No we know what not to do but how about what we can do? Lets consider a scenario in the moderate climate. It's preferred to start of with either a coal- or a passenger/mail-line. The distance between the two station should be moderate, say 30 squares **!
This way we still have some money left for rolling-stock and towards wages for our staff! (Does it show, yours truly being a former ticket-window clerk and traindispatcher?)
**! Here I disagree! 60 tiles is 'moderate'; 30 tiles is short! Rails are cheap! - My first project must earn well, and is never shorter than 60 tiles! - Cecilie

The advantages of the chosen cargoes are:
#1. good revenue (both cargo types);
#2. makes money on both legs (passengers/mail);
#3. no follow up needed (both).

#1. When the number of passengers and/or mail is very low you can initiate a bus service in both towns your railroad is servicing. This will create extra revenue for the trains. Rever to other websites for more tips regarding this topic.

#3. If we were to bring wood to a sawmill that mill will produce goods. Since we just invested all or most of our money we can't afford to put in another line to transport those goods. That results in a loss of council appreciation due to the produced but not transported goods. **#3
Now when we are ready to build in that councils jurisdiction we might not get all the planning permission we need. With coal you just bring in the coal. Nothing is produced so there's no council on your back. Unless of course you build in the vicinity of a town and do not set up a passenger/mail line.
**#3 If using TTdPatch: you can ask the station not to produce goods until asked for. So, no loss of council appreciation. Cecilie

When starting a freight-service it's best to have 2 trains (engines and wagons). Of course we will not use the maximum number of wagons at this stage, due to the output of resource and capacity of the engines. But instead of starting out with 1 engine and 4 wagons, choose 2 engines with 2 wagons each. Just the 1 train is not likely to transport more than 50% of the output where 2 trains usually carry out in excess of 75% of the production. Better council ratings and higher revenues!
I would use 1 train, 4-7 wagons and a 'piglet' truck. This works for both 30 and 60 tiles distance, and gives 75-80% production. Cecilie