君の実力なら楽勝だとは思うが、それに驕らず、まずはクラスのみんなと切磋琢磨していって欲しい。

tbd

I think you could easily win with your ability, but I want you to not be arrogant about it and work hard with everyone in your class first.

With your ability it should be a doddle, but please don't get too big for your boots: apply yourself diligently like everyone in your class.

驕れる者は久しからず。

tbd

Pride goes before a fall.

驕る平家は久しからず。

tbd

Pride will have a fall.