do (one's) level best

To do as well as one can at something. I'm just not good at math, so, believe me, a B- in Algebra means that I've done my level best. No, you're not the star player on the team, but you always do your level best, which encourages the rest of us to do the same. Once I saw how excited she was to finish in third place, I knew she must have done her level best.

level best, to do one's

To exert oneself to the fullest. A nineteenth-century Americanism, this term has been traced to the days of the California gold rush, when miners panning for gold would shake sand and gravel until it was level and revealed the ore. It appeared in An Arkansaw Doctor in 1851: “We put our horses out at their level best.” Mark Twain also used it, in a poem, “He Done His Level Best” (1875): “If he’d a reg’lar task to do, he never took no rest; or if ’twas off-and-on, the same, he done his level best.”