Nothing could be worse than it.
It couldn't be worse.
我是英语专业的,这两个说法都可以
I wish you would take on a new look这句话应该是对的,这是一个虚拟语气,如果对虚拟语气不了解,我这有资料可以发给你.或者你在百度上搜一下相关的语法知识