Get addicted to this game. The more you play the faster you will max your rank. (The maximum is 30 by the way.)
Complete goals. Completing goals will give you the secret weapon to levelling up. XP. That will increase your level meter. You can increase the amount of XP given by upgrading it in "My Stash".
Carry your game. Bring your device to work if you can. Then you can play while break time and can level up faster.
