i thought it best to tell her分析句子成分

i主语，thought谓语，it形式宾语，best宾补语，to tell her实际宾语。

主语+谓语+宾语+宾补，该句型中如果宾语是句子或不定式短语，应当在宾语位置上用形式宾语，把宾语从句或不定式短语放到宾补后面去，使句子变得稳定平衡。

I found (to finish the work in 2 hours) impossible.
I found it impossible to finish the work in 2 hours.

He thinks (that I leave today's work till tomorrow) wrong.
He thinks it wrong that i leave today's work till tomorrow.

宾语从句
主语：I
谓语：thought
it is best to tell her 充当主句的宾语，it做从句的形式主语，从句主语是to tell her

　　I主语,will tell谓语(will助动词,帮助tell构成一般将来时),her宾语,to wait for
you动词不定式短语作目的状语.