When I play an RPG, I like to get the feeling that the world is working: things
are how they are because they've come about for reasons that make sense.
To make a game-world where this happens, it's necessary to have some
idea of the basic economics of that world. This is best understood if
built from the ground up.
Take a science fiction world as an example. Suppose that given raw materials and
enough energy, people can synthesise just about anything. Raw building material is to
be found on planets, and the best energy generator is the fusion reactor, powered by
hydrogen. The most important economic resource is then hydrogen, which can be 'mined'
from gas giants (large planets made of impure hydrogen which occur in most stellar
systems).
If this is so, then the primary source of wealth in space is the gas giant. It's
rather like an oilfield in our world, except that there are no real rival sources of
power that can compete with it. This means that when people colonise an area of space,
one of the first things they do is to secure the gas giants and start mining them.
Once you know this sort of thing, the way the world works will just fall into place.
Power structures will build up around the control of gas giants. There will be
hydrogen refinery complexes orbiting these gas giants, which will be centres of enconomic
power. As a result, they will be heavily guarded, and people in power will keep tight
control over them. Economic war will revolve heavily around control over gas giants.
Refineries would be major targets for terrorists, because destroying them would cripple
a stellar system and plunge millions into freezing and starvation.
Refined hydrogen might become the basis of currency. A system government might own
hydrogen mining operations and trade stations throughout the system. Then it might issue
currency units, such that one unit can be reclaimed at a government trade station for a
fixed amount of refined hydrogen. Traders turn up at the trade station, sell their goods
to the government for currency, then spend some of that currency on hydrogen fuel. Any
currency left over can be used as money to buy things from other people.
This kind of understanding of the world is quite simple to achieve, but most people
don't seem to think about it, and that makes it difficult to make the world seem real.