首先分析一下句子：
It was good to see someone.这个可以作为一个完整的句子,it 代指 to see someone,这个句子可以改写为：To see someone is(was) good 动词不定式做主语.为了发出疑问,所以用how do you say 接上面的句子作为疑问句.
而且it is +adj(形容词)+to do something 是个很常用的结构,应该熟记
e.g.It is (really) happy to talk with my teacher.