In Halo 4, how does one level up there specialization that they've chosen after reaching level 50?

the question is really in the title. (oops.) Is there some kind of special assignment I have to do to rank up my specialization, or do I continue to rank up normally? (I picked Stalker, and I don't know if I should continue leveling up like normal, or if there's a specific task I have to complete in order to get the next Stalker "rank"... help?