give it my (our) best shot 尽力而为

Make one's hardest or most enthusiastic attempt, as in I don't know if I can do it, but I'll give it my best shot. This expression employs shot in the sense of “attempt”, a usage dating from the mid-1700s.

down in the dumps 垂头丧气

down in the dumps 

adj. very depressed and miserable. Synonyms: down, low, blue, sad

If you are down in the dumps, you are feeling very depressed and miserable. [informal] Example:

She's feeling a bit down in the dumps and needs cheering up.