To get this easily and quickly, do not worry about practice sessions(at the start of practice, skip to qualifying).
For ease, set the difficulty as low as possible. If you are confident of winning races on higher difficulties, don't worry about setting it low.
Make sure you qualify higher than your teammate, then make sure to either win every race or finish higher than your opponent in every race. Setting the fastest lap every race helps but doesn't matter as long as you set a faster lap than your teammate.
Follow that advice from the start of the season and you will be in "overachieving" in no time(i believe it's in the purple). Maintain that form until just over 3/4 of the way through the season and the achievement will pop.
It is most likely to pop in Mexico or Brazil