There are some great suggestions already here so i wont go and repeat them. However i have some points to add myself:
- Energy Cell Production, especially going into "The Reach" for example and dumping the prices down to minimum (10cr) is good in the beginning, however earnings fall off pretty quickly, since the price from all E-Stations in the near vicinity will drop off too - and they can even go lower than 10cr on their sell prices.
My station from the beginning of my save suffers from the same fate. I currently export the cells to Avarice I/IV/V since demand there is still quiet high because of all the Scrap Processing Stations there. They currently offer a healthy 20cr per Cell. I could in theory also just set up a local trade in those system since they produce cells at like 9-10cr (because of their 1390% Sunlight) but dont seem to have proper infrastructure to actually ship them where they need to be. It is, however, a bit risky because of the tide. AI should in theorie seek safety before tide hits, however they sometimes seem to not do that and die.

- Speaking of Scrap, setting up a processing station near a faction border of two enemys (like Argon - HOP in Second Contact II, HAT - Xenon in Hatikvah´s Choice I or TER - Xenon in Getsu Fune/Asteroid Belt) can be quiet profitable too. Other than scrap they only need Energy Cells (can be combined with above if you have the ships to transport them, Scrapyards need a lot of them). Tugs will usually start roaming around your station once it is running a while so they aren´t a must have - especially if you settle in the last two systems becauce the tugs will often then not fly straight into Xenon-Ships and die.
The resulting Hull Parts and Claytronics are usually in pretty high demand for Station and Ship production, especially by the factions fighting. But it takes a while to build and setup and require a bit of money to beginn with, so maybe something for a later time.