I think it +adj+to do正确还是I think it's +adj+to do正确呢

I think it+adj+that+从句 是固定搭配
I think it's+adj...也是可以的，它是I think 后面加从句。
是这个句型：It's adj+to do sth/that+从句。跟find差不多。
e.g I find it difficult to learn English well.或者 I find it's difficult to learn English well.两句句子的意思是一样的。不过相比较而言，前者更好。
在理论考试中如果出现上述情况，选前者；
在实际应用当中，两者都可以……

都正确，句式结构不同。
I think it important to study English.
本句think带复合结构， it是形式宾语，important是宾语补足语．
I think it is important to study English.
think 带宾语从句．

I think it +adj+to 对 it +adj+to do是做形式宾语的

后者