I've had a reasonable amount of success with carrying extra units of whatever a mission asked for to wherever the mission's destination is, especially when the unit price offered by the mission is high; the missions seem to usually be a good indicator that the goods being asked for have a relatively high price at the destination.
There was also a stretch where Mimir's trade kept getting disrupted, which caused the station to buy heavy machinery for about 300 to 400 credits before tariffs, and Ratatosk was selling heavy machinery for about 120 credits per unit before tariffs at the same time. Probably not healthy to abuse that situation too long since you'll end up ticking off at least one of your trading partners, but it did net me a tidy profit; by the time I stopped, I had added two Hermes-class shuttles to my fleet (sadly, nothing better was available on the open market, and I wasn't feeling that inclined to buy from the black market) and I'd gained about 100,000 credits even after deducting the cost of the shuttles (helped along by a couple of missions asking for heavy machinery, but it would have been profitable without those missions regardless).