在不定式标志to前加上not.例如：

Tell him not to shut the window.让他别关窗。

She pretended not to see me when I passed by. 我走过的时候，她假装没看见。

典型例题

1）Mrs. Smith warned her daughter ___ after drinking.

A. never to drive B. to never driver C. never driving D. never drive

答案：A.warn sb to do sth. 的否定形式为warn sb not to do sth. 此处用的是否定词never.

2） The boy wanted to ride his bicycle in the street，but his mother told him ____.

A. not toB. not to doC. not do it D. do not to

答案：A.not to 为not to do it 的省略形式。可以只用to这个词，而不必重复整个不定式词组。及物动词do后应有宾语，因此也B，D不对。