Definitely check that thread. But for quick help, my best piece of advice is: pay attention to how LARGE equipment is. This is indicated by the "cube" icon in the item's stats. Every item, be it a weapon, a shield, or even just a package you are delivering for a quest, has a different size. Even two identical items can have different sizes. You might have a photon gun of size 50, and then find another one of size 12. Use the size 12! Smaller equipment opens up space to carry cargo.
In the beginning, avoid fighting and try to do government quests whenever you can. These pay the best. If you can't find government quests, consider trading, following advice you hear on the news (be sure to check the news whenever you land!). You can use the "paperclip" icon to save any news item, or any other text box for that matter, onto the bar at the bottom of the screen. Then you can view it again later.
Another way to get money is to sell Klissan equipment. If you hear about some Rangers fighting with Klissans, consider showing up, but DON'T fight anything. Instead, just grab up all the Klissan equipment and proroplasm that's been scattered around and then run away. You can sell the equipment to science stations in order to boost their research, and you can deliver the protoplasm to Ranger stations in order to gain points you can use to increase your skills.
That should get you started. For more detailed advice, check the thread that HereForTheBeer linked to.
Oh also, reading the manual helps a lot, if you haven't checked it already. It's in PDF form in your install directory.