Aim for at least 1000 Cr/Ton on trades routes, there are plenty of commodities you can do this with.
Trade circuits are more fun than endlessly grinding back and forth, bellow is one of my favourite, all the following can yield 1000 Cr/Ton per leg.
Industrial - Pick up Marine Equipment / Crop Harvesters)
Agriculture -Pick up Tea, Coffee, Meat, Tabaco or Imperial Slaves (If legal)
Refinery - Pick up Gold, Palladium, Beryllium, Silver, Super Conductors.
High Tech - Pick up Auto Fabs, Consumers Electronics, Performance Enhancers.
Just keep at it, don't get to concerned with progress - have fun with it, at least you won't be burning out on the games content like so many others.
Absolutely right! Find the style that makes it fun for you. Doing the same thing over and over gets old quick. Running rares allows you to stop and explore, make a trading profit, and kill the occasional stupid pirate. All in the same trip. The ASP is perfect for that, but you can get pretty close with the Cobra as well. I never look at the balance sheet until I'm done having a good time.