My first question is what do you want to do ? A) have fun and discover B) get some help C) Max out your profit
A) In the commodities screen, the last column is useful: it can show what commodities are imported or exported and to/from which system.
Of course they only show a few and more lucrative roote might exist. Are you in the game to maxout you Cr or to have fun ? Go out and try.
B) In second, I certainly recommand
this infography to have nearby on your secondscreen (pc or tablet) By the way if any one konw abouta similar infography that in "ink" friendly (It would be great to print it out and have it in paper form).
This is a sort of generic but realistic and immersive way of doing trade based on the type of comodities that type of systems.
C) And last but least, they are external tools that exist on the internet like
eddb.io and
www.elitetradingtool.co.uk/. Other tools exists of course. After some unsuccessfull trade route I eventually started using these tools. For a while this is fun, It helps you to acquire more rapidly precious credits to play with other modules and ships. Rapidly though, it becames evident that this is killing the fun (doeing ABA route, again and again). I reverted to A) or B)
Now I seldom repeat trade routes (or just a few times). I rather mix them with other self-established goal like go from system A to system B and find a commercial route by yourself, Exploir possible route from a system C or to a sysem D, try to dock to a different station more often, etc
Have FUN !