什么时候是not do什么时候是not to do?

如果一般搭配是to do, 那么否定就是 not to do
一般搭配是 do, 那么否定是 not do

一般来说大部分名词,形容词和动词都是和不定式to do搭配的, 只要记住特殊的 do 就可以了
do类:
Why not do, (但是一般文体和正式文体中不能说why do, 只能用完整形式 Why do you .., why does he ...等等；换句话说，日常对话的非正式文体中可以存在why do)
情态动词 + do (would do, can do, shall do ...)
had better do, had better not do
prefer to do rather than do (一般不在这里放not)
see/watch/hear sb. do (一般不在这里放not)

would是情态动词，后面接动词原形，否定形式在would后面接not就行了。
例如：i would come. i would not come.=i would`nt come.
但是would like的话后面就要加不定式了例如：i would like to have a cup of tea. would you like to come with me?

应该是would not do吧.
would better do.
example:
I would't help him if I knew he was such a person.
you'd better finish it tonight,or you'll lose the chance.