A some-what safe route would be Tulir to Ariane. Buy medical supplies on New Riga in the Tulir system and sell them on Telnan in the Ariane system. The two systems are right next to each other. Every now and then, Telnan will raise the price of medical supplies, so you get a major profit on when that happens. If you have hired 6 Marinu Heavy Freighters, you will get a profit of about 440,000 credits per return-trip. That's not too impressive compared to other routes, but you will get something like 2 million credits (profit) if the price on Telnan is raised (it will say "higher"). It's amazingly satisfying to sell at such a price.
If you're feeling dangerous, you can also trade metal on the return trip, but I don't recommend it because the price of metal on New Riga often goes way down (it will say "lower"). It's just too risky. Besides, you don't make much profit for it, and you'll just wear out your mouse button that much faster.
This is, in my very humble opinion, the fastest (in terms of real-life time) and easiest way to make money. I even like it better than the Saalian Brandy route.
Another way to make money is to get a badass ship and disable board Renegade vessels. You get a high combat status and social standing in the process, not to mention possible escorts.
------------------
"I like ice cream without chunky bits in it... they get stuck in my tubes." — Bungie's Soul