it hard to improve listening 是省略句,做 find 的宾语.to improve listening 不定式是省略句的实际主语,it 是省略句的形式主语.整个句子还原是：I find (that) it (is) hard to improve listening.省略句主语还原是：I find (that) to improve listening (is) hard.
to play the piano 是 likes 的宾语.
important 做表语.for us 行为人（主语）.to look.是整个句子的实际主语,it 是形式主语.