I think I have found the shortest profitable two-way trade route in EV:O 1.0.2. It isn't very profitable because you buy for medium and sell for high on both places, but it's incredibly quick. The endpoints are so close you essentially just have to turn around to land. I can't remember what the commodities are (metal and equipment maybe? Maybe not...) but I know the prices and locations.
I started a new pilot to try doing things in a different order from what I have done before. I took my shuttle and, without doing any missions or fighting or trading or purchasing or anything, flew to Emalghion in a circuitous route stopping at Outpost Theta, Station Pybin, and a couple other places on my way.
Anyway, I landed on Emalghia and went to the bar, where I accepted the mission to defend the system from the Voinians. I didn't have to do much work, thanks to the Emalgha ships in the system. I only had to take out a single Voinian Cruiser by myself in a stock shuttle, which is easy enough.
That done, I landed again, collected my 150,000 credit pay, and immediately bought an Emalgha Fighter. I accepted the dimplomacy mission from the second moon of the planet and went back to Earth. I wanted to accept the diplomacy return mission, but that annoying UE Shipping Recruitment mission kept popping up first, and I didn't have the cargo space to accept it. I bought a Shuttle, accepted that mission and then the mission I wanted, aborted the shipping mission and flew back to Emalghia.
Bought another Emalgha Fighter and did some more "defend the system missions". Went to UE space to get Blaze Cannons instead of Emalgha Cannons. Came back to Emalghion and hired some Emalgha Freighters. Started trading to earn money.
The trading takes place entirely within the Emalghion system. Buy at medium price for 240 on Lmeito and sell for 300 on Emalghia, then buy for 480 on Emalghia and sell for 600 on Lmeito. Rinse. Repeat.
The "rinse" step is all-important. Don't omit it. Watch out for Voinian raids that jack the price on Emalghia up from 480 to 730 though. It usually only lasts a single day so you don't have time to buy for 600 and sell for 730. Just keep trading the other stuff and it'll revert back to normal pretty fast. I earned five mil right quick doing that. Got some engine and shield upgrades on my Emalgha Fighter, and am having lots of fun. My combat rating is already Ultimate. I think I'll join the Zachit next...