@Miles
To go fully manual:
Each commodity says which economies produce it and which consume it. For example, high tech make prog cells, and everyone wants them. Industrial likes tobacco and liquor, and metals, etc.
Fly to a random station, check which high supply commodities are worth more than 5k, and are selling for at least 500cr less than average. Check map for economies nearby that should consume that good. Buy 1 of everything interesting, fly to target system and see if you made good choices.
With a little automation, but all own exploration:
Same as above, but type prices into android app Elite Notes. Let the app highlight good trades from the data you've entered.
Using method 1 above, I found many 500cr /t trades. Using method 2, I found a 1 jump 2000 cr/t route in 1 evening of playing, entering prices for 6 nearby systems. Good routes are all over the place, especially extraction - industrial locations where you can haul palladium or platinum with a small percentage mark up. But running weapons, slaves, and some machinery can also be profitable if you find someone who wants them. Don't be afraid of occasionally running illegal goods to Fed outposts with black markets.
I find doing the exploratory work myself makes trading less of a grind, and much more rewarding.