Trade routes are always a good way. I'm sure some of the more...experienced traders here would LOVE to help.......

Well, there really isn't much to it. Just pay attention to the prices of goods at different bases. Buy cheap and sell expensive. It's not percentage that is important, but actual income per ton. (buy 100 sell 120 is better than buy 1 sell 19, unless you lack the funds to fill the ships cargo space). At first, if you're only traveling a short distance, you'll only get a small profit per ton. Later on, you can earn a lot on trading. I haven't done much missions, but it seems to me that trading might be the best way to earn cash fast. The danger with this is that if you do a lot of trading and get 2 million or so with the best cargo ship, you'll be the highest level and there wont be much else to do. I was very focused on getting cash fast, it was what I found challenging and fun in the game after the story line, but once I hit level 38 it was essentially "game over" for me.