Easy enough. I've actually done it twice. The second attempt little a little smoother. For both, I started out by doing two (difficulty one) kill missions, then traded in my light fighter for a Rhino.
In my first attempt, my next goal was a Mule. It's hard to tell you how I did that without resorting to spoilers, but I'll try. Basically, I pissed off the Bounty Hunters, and in the process made a ship-load of money. I ended up selling it for a heavy fighter, until I could clear up my rep with the bounty hunters. After that, I switched to a Clydesdale, then a Drone, a Humpback, and finally the Dromedary. My trade routes have made me wealthy enough that every so often I indulge in a VHF for a bit of exploring before returning to the Dromedary.
For my second attempt, in order to avoid spoilers, I won't tell you where I traded. Suffice to say it was a simple route in the New York system. Each haul netted me about 2000 credits profit. From there, I reversed course by buying a Legionaire light fighter. Believe it or not, this was my new freighter. I loaded it's cargo hold, and used it as a "blockade runner." Where big freighters have to rely on their shields, armor, and turrets to hold off attackers during a lane disruption, the light fighter runs circles around it's ambushers until the trade gate is ready. My light fighter ran the trade routes in good time, without ever losing a cargo. I just upgraded to a Valkyrie, and I hope to continue the work. It's like FedEx in space, "for when you absolutely, positively, have to get it there overnight."