Ⅰ、动词不定式中的省略
1．在下列动词see ，watch ，notice ， observe ， look at ， make ， have ，let ， hear ， listen to ， feel等后的不定式做宾补，要省略不定式符号。
2．在．．．do nothing but / except do ．．．的结构中，在介词but或except后作宾语时不定式符号要省略。
3．在would rather和had better后不定式符号要省略。
4．在几个不定式并列时，第二个、第三个不定式的不定式符号要省略。
5．在expect ，forget ， like ，want ， wish ， try ， have ， need ， used ， ought ， be able ， be going 等动词和动词词组后接的不定式中，不定式符号后面的动词原形常省略。
Ⅱ、从句中的省略
1．在if ， as if ，while ， when ， where ， although ， unless ， what ， whether等引起的状语从句中可以省略主谓部分。
Mistakes， if any ，should be corrected ．（ = if there are any mistakes）
Please come again ，if possible．（= if it possible for you to come）
Fill in the proper articles where necessary．（= where they are necessary）
He wont come ，unless invited ．(= unless he is invited)
He opened his lips as if to say something ．（= as if he were going to say something）
2． 在if引起的从句中如有等词倒装时，省略if。
Were I you, I would not do it.
Had we known your telephone number, I would have given you a phone call.
3． We have finished our homework, so have they. (= and they have finished their homework , too)
If you dont go to the concert, neither shall I. (= I shall not go to the concert either)
4．宾语从句中连词that引起的宾语从句和定语从句中的关系代词that、which，whom等
在定语从句中作宾与可以省略that。
Ⅲ、介词的省略
prevent sb (from) doing sth.
stop sb (from) doing sth.
have trouble / difficulty (in) doing sth.
spend time / money (in) doing sth.
be busy (in) doing sth.
Ⅳ、替代
省略与代替的作用是什么?
1．so代替前面句子中已经表达过的词,短语或句子(多是宾与从句). 与so 连用的常用动词有：hope , believe, think , be afraid , expect , surprise, imagine等．
2．用not代替so的情况.
3．用不定式符号代替不定式.
4．用do在句子中代替其它动词.