1.若主句主语与从句主语一致，而主句的谓语动词为hope/decide/ wish/choose/agree/ promise等，则从句可简化为不定式
I hope that I will succeed.
→ I hope to succeed.
I have decided that I will accept the offer.
→I have decided to accept the offer.
She promised that she would be back.
→She promised to be back.
2.若主句主语与从句主语一致， 而从句的引导词为代词（如who, what）或副词（如when, where, how）等时，则从句可简化为“疑问词+不定式”
She knows what she should do next.
→She knows what to do next.
She knew where she would live.
→She knew where to live.
He remembers how he can open the door.
→He remembers how to open the door.
Could you tell me how I can win the contest?
→Could you tell me how to win the contest?
Have you taught her what she should do?
→Have you taught her what to do?
The commander ordered that we should set out at once.
→The commander ordered us to set out at once.
They require that I should be there.
→They require me to be there.
4.某些动词后的宾语从句可简化为“it + 形容词 + 不定式短语”
She thinks that it is important to finish the homework.
→She thinks it important to finish the homework.
He found that it was difficult to convince her.
→He found it difficult to convince her.
He doesn’t understand what she says.
→He doesn’t understand her words.
He has told me how I can get to the station.
→He has told me the way to the station.
She doesn’t know when she was born.
→She doesn’t know the time of her birth.
She found that there was a dog lying on the ground.
→She found a dog lying on the ground.
She saw that the dogs were running after a rabbit.
→She saw the dogs running after a rabbit.
I remember that I have closed the door.
→I remember closing the door.
She forgets that she has called him.
→She forgets calling him.
She found that the road was covered with fallen leaves.
→She found the road covered with fallen leaves.
The detective found that the man was killed in bed.
→The detective found the man killed in bed.