I haven't really run too many general commodities, however I use the
"Trader's Bible Infographic"
http://imgur.com/gallery/QsxScn1combined with ed-td.space or inara.cz for quick information on the systems and stations
from there, it's what one would want, vs what one normally sells - and buying below GA, and selling above it!
best profit I've gotten in a one-way trip was with coffee from I Bootis to Az Cancri at 1500 cr/t.
normally I run rares though, and for those I use
eliteraretrader.co.uk to map out my route (I like to change it up instead of the same-old same-old)
edshipyard.com has a wonderful route planner on the side. I use that with a saved URL for my ship to optimize the ship for the trip so I can make the longest jump without getting more fuel. To put it plainly, if my ship can't make the run, I don't do the run.
here's an example:
this is the Adder I'm currently flying -
http://edshipyard.com/#/L=70f,mpV01Q0Wg ... U7OW03w5AAwhich although it has the
ability to haul 20T, I make sure she only has 18T to make sure she can make the run from Az Cancri to Arouca