The leveling system in this game is a collective between the 4 categories of sub-levels. These Sub-Levels are different varieties to make way through the game.
Competition - By gaining licenses, winning championships & cups and multiplayer challenges.
Collection - By collecting cars, houses, clothes and even getting haircuts will advance this skill.
Discovery - By driving on roads, collecting wrecked cars, taking photographs and completing missions will advance this skill.
Social - The Multiplayer skill which is raised by catching outlaws or escaping the cops in chase modes, playing co-op races, setting up races, playing a part in a club and simply by having friends.
At the moment, including the DLC there is a maximum level of 70, making this achievement very easy to obtain. However, if you do not have the DLC then this achievement is very tricky indeed.
To check your progress on your levels, hit the button then for the "Progress & Objectives" menu. Inside here you'll see your "Global Level" and each of your 4 category levels. Hitting either or will allow you to have an overview of each category and requirements to gaining the levels necessary.