This achievement requires you to play pro club seasons which requires a minimum of two people. You will play against human players in other clubs of their own. As the achievement states you need to unlock 10% of all accomplishments. There are, to my knowledge, 311 online pro accomplishments. You will receive the achievement when the accomplishment counter reads at 10% which could potentially be less than 31. These will come naturally through gameplay against the other clubs providing you aren't terrible at the game. There is a boosting method though.
Boosting online pro accomplishments.
Make a Pro Club with 1 other person.
From the Pro Seasons Menu, highlight Drop-In Match. Communicate with your friend and make sure you search for a Drop-In Match at the same time.
Hope you get each other alone and if you do, ready up on different teams then both select the ‘Any’ position unless one of you wants to get Goalkeeper Accomplishments.
Start the match and unlock FIFA 13 Accomplishments!
Credit for boosting method goes to blameyourany.com