Its for sb.和 Its of sb.区别解析与判断
1）for sb. 常用于表示事物的特征特点，表示客观形式的形容词，如easy, hard, difficult, interesting, impossible等：
Its very hard for him to study two languages. 对他来说学两门外语是很难的。
It’ s very important for you to solve the problems.
解答出那些难题对于你来说非常重要.
Its important for us to study English.学习英语对我们很重要。
2）of sb的句型一般用表示人物的性格，品德，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。kind、wrong, clever, careless, polite,
Its very nice of you to help me. 你来帮助我，你真是太好了。
It’s very nice (kind,friendly) of you to help me carry the baggage.
你真友好,帮我搬了行李.
Its kind of you to help me.你能帮助我真是太好了。
for 与of 的辨别方法：
用介词后面的代词作主语，用介词前边的形容词作表语，造个句子。如果道理上通顺用of，不通则用for。如：
You are nice. (通顺，所以应用of)。
He is hard. (人是困难的，不通，因此应用for。)
总的来说，for sb.的结构是指这件事对于某人的作用或意义，而of sb.的结构是指发言者对行为者的主观评价和看法。
注解：这两个词最比较好用的辨别方法：如果be动词后的形容词是说明不定式的逻辑主语,就用of sb.to do...；如果是说明整个不定式的,则用 for sb.to do...；例如：
1.It is very kind of you to help us.（可以转换成：You are very kind to help us.kind说明 you 的属性）；2.It is possible for us to get there before dark.(不可转换成：we are possible...,而应该是 for us to get there is possible)