For a solid 100 Gamerscore just win the world cup in captain your country mode. I find being a striker with Spain is the easiest route to the final and therefore winning this achievement. This is because Spain are the best team in the game and thereby you have the greatest chance of winning the tournament whilst being on their team. As a striker you are not at risk from conceding silly goals due to your own errors. You can complete this achievement on any difficulty, which is handy if you are not the best virtual footballer. Good luck all.