Flying around in a non pimped Buster, with two Impulse Ray Emitters, getting missions to blow up random trade ships for 1000 credits. Which is to say, it's going really slow.
If you see them send a surrender message, make sure to stop shooting. They'll bail out and you can take their ship. It will come to a stop and be neutral. You'll have to bail out of your ship in your space suit and get close to your new acquisition. From the right lick menu there will be a new option, Claim, once you are close enough. Make sure that you tame the ship with Claim before you zap it with your healing laser (like a unicorn). Also I'd recommend waiting until you blow up everyone shooting at you.
You can even repair it back to full hull with your space suit laser, so that it will be useful. After that, either switch to that ship and haul goods around until you can outfit the cargo ship with the trade and navigation computers and stuff that will let you do purchases and navigate said purchases to a buyer. Speed and maneuverability upgrades should be the first priority, followed by cargo space before it starts getting very expensive.
After that, the hardest thing to do is to remember to send that ship around to buy and sell stuff. You probably won't lose very many, or at least not until they've paid themselves off.
Also, once in a while ships flying around with the cents symbol will offer to sell you their ship as they are buying a new one. The price seems to be random, with some asking dirt cheap prices for a ship that you can sell to the shipyard for several times what you paid after you've blasted it with repair laser for a minute or two. It's worth comming ships and stations with the c for cents symbol.
If you have a small, fast ship that can hold a few hundred cargo, consider space weed. Unfortunately, you will be lucky to find a Space weed factory that has produced enough to be able to sell it at a profit since a place to sell it usually is a Teleri space station, which only buys 40 units, or a Pirate base on the pirate infested sector bordering Xenon Hell 59 and just the other side of Argon Police Academy.
Basically, just buy whatever from whichever station is maxed out and can't produce any more, thus cut rate prices. However, be very careful of race specific goods in particular as you will be somewhat confined to that race's space until you offload the cargo.
A very easy and simple way to make money is in systems that are lucky enough to have an ore mine in the same system as a factory that uses ore, which is almost every non agricultural building. The thing about ore is that it's value is low while it's bulk and size is very high. This means NPC merchants often times will ignore even inter-sector trade. Since ore is produced quickly as long as there is energy (which you may be able to supply) you can make quite a few lucrative trips supplying the factories which will likely be unsupplied. However, bigger ships are better as you can sell more at once so that you fill up their demand. Then you won't need to settle for a lower the price for the next shipment.
This is unmodded by the way.