It is useful for us to learn English well.
记得初三英语学的这个吧 书上有两个用for的例句：
It is easy to have a healthy lifestyle, and it is important to eat a balanced diet.中间都可以加上for us（放to前面）
再给你个例句：It is necessary for us to sleep well.
下面是用of的例句：It is kind of you to help me.(你能来帮助我你是善良的)
发现了吗,用for和of是不一样的,of表示的是of后面接的那个sb的本身的性质,比如可以是kind,friend,nice之类的.好好体会一下,不难理解的.
希望对你有所帮助.
