Found this post on the topic of Piracy.
It's not too complicated in theory. The best targets are in Agriculture systems in boom. Every miner (ships carrying a mining laser) in supercruise carries low temperature diamonds.
There are also private couriers, which I think can appear everywhere, these are usually carrying a medium amount of valuable goods.
Now the difficult part is the actual piracy. These targets will always try to run, sometimes using mines to get you off their six. You need to react quickly after the interdiction. You'll also want to use a weapon which can strip shields fast, but is less useful against hulls. Fixed beams are great for this. After the shields are gone, you have to target the drives to disable the ship and keep it from running, but you have to take care not to kill your victim. Not all NPCs are capable of rebooting, which means they are dead in the water, but still moving with their original velocity. The only way to stop them is to carefully overtake them and reducing your speed to zero (with FA on to slowly brake). This will usually take more than one try, but you will notice them going slower. Try to avoid ramming them, as this can kill your target.
Now, when they are finally moving with less than 50 m/s, you use hatchbreakers and collectors. But it's not over, head over to eddb and find the system with the best LTD prices and make sure that they have a black market. This might take you hundred lightyears, but a price of 900.000 per ton is possible. It will be a smuggling run and you might have other NPC pirates on your heel, but depending on your ship the payout will be huge.