How can I be a successful trader?
Solution 1:
From my limited playing of E:D so far there's a couple of ways of getting improved profits per tonne, although ultimately the best way to do it, is work towards larger cargo modules and also larger ships.
The first option is just to work on finding the most profitable commodity to trade from a specific station. For that, the best way I've seen is to use something like the Elite Trading Tool, which allows you to enter a starting station and other variables and gives you the best routes that it currently knows about. These aren't always perfect, but generally I've found they're better than just using the in-game tools.
Another option is to trade "rare" goods. These are specific items which are available at some stations and which get considerably more valuable the further away you take them. You need a decent amount of cash to start doing this (to pay for fuel to get far enough away to increase the value) but you can make considerable profits with the right route (e.g. with a 40 Ton Cobra, I made ~500,000 each way on a run).
The trick with rares seems to be finding good clusters of items at either end of a run. For example this one
Solution 2:
I'm by no means an elite trader but if figured out how to make one to two thousand credits a trade with the starting ship. Part of that has been done using this info graphic here http://i.imgur.com/QsxScn1.png which I use to plan my routes a bit. Basically at whatever station your at go through the items for sale and compare the buy price to the galactic average. I usually try to find an I've. With three hundred or more profit ratio co paced to galactic average. Then when my cargo hold is full I plot a route to the nearest station that's outside the export are a of the station I'm at, that wants that type of item according to the info graphic. Which is usually a minimum of four jumps away for best profits. Then I just do that over and over, bonus if you can combine it with a mission to get something for someone from some distant system.