I tried to start a normal career mode game, totally don't have any idea how to make money. :P
Use contracts to complete simple things, like testing prototype parts, or taking tourists on a flight.
Also, try to attach parachutes and things to as many detachable stages as possible, so that they survive their way back to the ground.
That way you can collect them again from the Comms Array thingie, and you get money back.
Every piece that crashes into the ground and explodes is wasted money.
Also, there's that marketing place building where you can trade resources for each other, such as science/reputation for money or vice versa.