Use healer
With Aura you can place a healing station where people can heal if you place it close to the battle field or half in to it people wil use it in batlle and get damdged and instand heal in your station so you get fast much xp if you play it smart.

Play objective
you get 1000 XP for letting a bomb explode at the objective,
or do other objectives.

Play something that you're good with.
If you can make a lot of kills you get also a lot of XP.
(Pro tip: Aim at the head.)