it is important for sb:water is important for human :水 对于人来说 很重要.
it is important for sb to do sth:it is important for us to drink water:对于我们来说喝水很重要
it is important to do sth.:it is important to drink water when you're extremely thirsty：当你极度口渴的时候,喝水时很重要的.
另外单独用的比较常见的就是,it's important to me/sb.这就已经是完整的一句不会有变化了,就是说对于某人来说意义重大或者理解为it means a lot to sb的意思.一般都会在上边交代清楚内容之后,来用.My dad used to teach me how to fight.It's important to me.
不知道是否适用