A suggestion that MIGHT help get more credits is to wing up with a friend, if you can (especially if they have a large ship capable of carrying a lot of cargo). Then, when they sell their cargo (provided you are at the same Station they are at when they sell) you will get a Trade Dividend from the Station worth 5% of their profit margin. 5% may not sound a lot, but when I pop into Starter Space with 384 tonnes of Performance Enhancers each new Player who is in my Wing typically gets 24Kcr Trade Dividend. That is enough to get them a 2C FSD. The biggest TD I have seen is when I was working a Community Goal, and the Station was paying well above the odds for the materials required, and then the TDs were 80Kcr per Wingman.
I would also suggest that, in future, you make sure to have 200% (at least) of the purchase price of a ship before you buy it. That way you should have enough for the ship, some basic outfitting, a couple of cargo loads, and a couple of REBUYs (just in case). If you are planning on selling a ship make sure to take it back to factory standard first. You will always take a 10% hit on the value of the ship at the time of selling. However, if you sell the modules first (replacing a 2A FSD with a 2E FSD) you will get back the price you paid for it (currently, at least, although this may change in the future). Then, when you sell the ship, your losses will be reduced. For example, I have a fully A Rated Cobra MkIII worth 10Mcr. If I were to sell her as is my losses would be 1Mcr. If, however, I take her back to factory standard and then sell her my losses would be 35Kcr.
I would also suggest that, in future, you make sure to have 200% (at least) of the purchase price of a ship before you buy it. That way you should have enough for the ship, some basic outfitting, a couple of cargo loads, and a couple of REBUYs (just in case). If you are planning on selling a ship make sure to take it back to factory standard first. You will always take a 10% hit on the value of the ship at the time of selling. However, if you sell the modules first (replacing a 2A FSD with a 2E FSD) you will get back the price you paid for it (currently, at least, although this may change in the future). Then, when you sell the ship, your losses will be reduced. For example, I have a fully A Rated Cobra MkIII worth 10Mcr. If I were to sell her as is my losses would be 1Mcr. If, however, I take her back to factory standard and then sell her my losses would be 35Kcr.