At its heart, Age of Steam is a fairly simple game. While the rules change from map to map, over 90% of the time the winning strategy is the same: set up your tracks and build up your engine such that you can start making 5- and 6-point deliveries as soon as possible.
Early on, it can be difficult to justify the expense of increasing your locomotive. Unless you can get the increase locomotive action (which requires spending money to get into the top two spots and passing on Urbanization), you have to give up a delivery just to up your loco by one. That’s between one and five income that you don’t get, as well as another dollar added to your expenses each turn. Additionally, at the start of the game you’re already in the red, so adding to your expenses just makes it that much harder to dig out.
However, try looking at it from the other direction. By increasing your locomotive early on, you’re giving up a point of income now, in exchange for potentially getting another one to two points of income every turn for the rest of the game! If anything, it gets harder to justify the increased locomotive once you’re up to three or four, as you’re now giving up more income and have less time to recover it. Even though it costs you money, bumping your locomotive every turn for the first few turns is pretty much a no-brainer; it’s sure to pay off later.
Provided, of course, that there are longer deliveries to be made! A common rookie mistake is to separate your track, putting pieces in various areas of the board; while that might let you grab more easy deliveries at first (and annoy your opponents), it means that you’ll be limited in how far you can ship goods without going over your opponents’ track.
One thing people may not realize it that increasing your loco by one doesn’t have to mean just one more point of income. It’s not uncommon that at the end of the game there will be deliveries that cannot be made in less than six links; having the one last point on your locomotive can mean the difference between getting that six and having to settle for a two on the last turn!
One tactic that I use on some maps is to build a large (say, 6-9 links) loop around the board. While a cube can never re-enter a city it’s already left, having a loop like this gives you multiple ways to make the delivery; for example, the loop might contain only one blue city, which is only 2 links away in one direction but a full six in the other. Chords (track that cuts across the loop) are also useful for avoiding cities you don’t want to enter (for example, a city might have a red city on each side of it in the loop; taking a chord allows you to move the red good from that city around the loop before delivering it).
Having multiple pieces of track coming out of a city can also help protect your cubes; each city has at most six ways into it, so the more of those you can block off, the harder it is for your opponents to get in and steal the cube you wanted to deliver (or deliver to that city). Practical example: on the Ireland map, which has two red/blue cities and no other way to deliver red or blue cubes, I once overspent – forcing myself to go down on the income track – in order to claim all paths to those cities. I more than made back the lost income as for the rest of the game, my opponents could only deliver red and blue cubes by moving over my track.