So as the description says. You need to finish the race 12 positions higher than where you started. If you qualify in the top 12, this achievement is already impossible to obtain.
The easiest way to get the achievement is to simply spend your time practicing and skipping quali completely. This means that in a normal race you will start around p20. Then stay clear of the chaos and with a bit of luck and skill you should be able to finish p8 or better quite easily. Took me 3 races to get this achievement done this way.