Heart of the Swarm beta is getting a new patch which will feature a new leveling system for the game. The leveling system will follow each race, that is mastering one race will reward players will new decals and portraits.
These rewards off course come with the usual bragging rights and enforcing fear into the hearts of your opponent where they will not look at you as Level 15 Bob, they’ll see you as Bob who has mastered the Zergs.
For leveling you just have to play in either Blizzard’s matchmaking or custom games which in turn will grant you XP (More for wins and less for losses).
It’s expected that a ‘First Win of the Day’ feature will also be introduced where you get double the amount of XP for your first win in the day.