There's a piece of Callisa's armor you receive as a daily reward. Each piece gives a +5 bonus to your energy and stamina, as well as increasing your hp by 50. Don't know when the daily rewards are going to return to normal though.
And also Callisa's armor gives you PVP bonus. You can find a variety of things during the game that increase these characteristics. In my opinion the quickest way to levelup is with stamina so...