Bié zhěngtiān xiàng ge sàngqìguǐ shìde, zhènzuò diǎn.
Don't mope around like a sad sack all day - pull yourself together.
Tips
register
Colloquial. The 鬼 'ghost' suffix is a common Chinese way to label types of people (酒鬼 drunkard, 烟鬼 smoker, 懒鬼 lazybones) - usually mocking but not seriously offensive.