Instructions
Use all of the weapons and equipment in your inventory. Every time you kill a certain number of opponents with a different weapon or item, the game will reward you with free experience points.
Click on the "Barracks" icon in your main menu and review the objectives you can complete to receive experience points. Select objectives you can quickly achieve, such as "Basic Training" objectives.
Use the "Headquarters Pro" multi-player game mode to gain additional experience points. This game mode allows you to kill more opponents than other modes, thus enabling you to earn more experience points in the same amount of time.