There are lots of different ways to maximize the amounts of experience points you receive within the game. I would suggest purchasing Premium account time from the Shop (use this article for help doing so), as it multiplies the amount of experience you receive by 1.5x, and it also gives extra crystals too.
I would also suggest playing modes such as Capture the Flag, Rugby, and Team Juggernaut, that have a specific objective, as completing this objective gives a very good amount of experience points (for example, capturing a flag in CTF mode gives 15 experience points, which is more than the 10 EXP you get for a single elimination). You can find more information about the EXP system here.
Hope this helps!
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