一、選準關係代詞和關係副詞
在定語從句中，關係代詞或關係副詞都代替先行詞在從句中充當一定的成分，如果該從句中缺少主語、表語、賓語或定語，就要用關係代詞來連接從句；如果從句中缺少狀語，就得用關係副詞來連接從句。例如：
(1) I still remember the days which / that we spent together.
(2) I still remember the days when we worked together.
二、瞭解僅用that 引導限制性定語從句的幾種情況
that 在限制性定語從句中既可指人又可指事或物。在下列情況下，只能用that 來引導定語從句：
1. 先行詞是all , much, few, little, everything, anything, nothing 等不定代詞時。例如：
Is there anything that you want to buy?
2. 先行詞被all, few, little, much, every, some, no等詞修飾或被the only, the very, the same, the last 等限定詞修飾時。例如：
These are all the pictures that I have seen.
This is the very dictionary that is of great help.
3. 先行詞既指人又指物時。例如：
My father and his teacher talked a lot about the things and the persons that they could remember.
4. 關係代詞在定語從句中作表語時。例如：
Our school is not the one that it used to be.
5. 先行詞被形容詞最高級或序數詞修飾時。例如：
This is the best English film that I have ever seen.
The first English novel that I read was A Tale of Two Cities.
6. 主句是who 或which 引導的特殊問句時。例如：
Who is the girl that is standing under the tree?
Which is the machine that we used last Sunday?
三、把握“介詞＋關係代詞”結構中介詞的選用
介詞的選擇與主句中先行詞的搭配密切相關。例如：
That's the reason for which he was late for school.
This is the book on which I spent 8 yuan.
注意：
1. 定語從句中謂語動詞是含有介詞的動詞短語時，介詞應放在動詞之後，不能拆開放在關係代詞前。例如：
This is the key which you are looking for.
This is the baby whom you will look after.
2. 該結構中，關係代詞指人時用whom，指物時用which.
四、弄清as 和which 引導的非限制性定語從句指代整體時的區別
1. 位置上的區別：as 引導的非限制性定語從句的位置比較靈活，可以放在主句前，也可以放在主句後，還可插在主句的中間；而which 引導的非限制性定語從句只能放在主句之後。例如：
As is known to us all, the earth turns around the sun.
The earth, as is known to us all, turns around the sun.
The earth turns around the sun, as is known to us all.
The earth turns around the sun, which our parents once told us when we were very young.
2. 詞義與聯繫上的區別：as 引導的非限制性定語從句與主句之間有著較為密切的上下文聯繫，as 本身含有“正如”之意；而which 引導的非限制性定語從句與主句之間在邏輯意義上近似並列句，which 本身表示“這”或“這一點”之意。例如：
Light travels faster than sound, as we all know.
Jack came late for school, which made his teacher angry.
五、注意定語從句的主謂一致性
關係代詞在定語從句中作主語時，從句的謂語必須與先行詞保持人稱和數的一致。例如：
Tom is one of the boys who are from the USA.
Tom is the only one of the boys who is from the USA.
六、保持主句的完整性並避免從句成分的重疊
1. 在定語從句中，不管出現任何情況，主句的結構必須完整，即主句必須有主語和謂語，缺一不可，否則，整個主從複合句就無法成立。試比較：
(1)Is this factory _______ we visited last week?
(2)Is this the factory _______ we visited last week?
A. which B. where C. what D. the one
分析：
第一題缺少表語，只有填D項才能保持主句的完整性，而其他的選項均為干擾項。
第二題主句本身完整，應填的關係代詞在從句中作visited 的賓語，故應選A項。
2. 從定語從句中，關係代詞或關係副詞已經代替先行詞獨立地或與相應的介詞一起在定語從句中充當了一定的成分，因此在定語從句中就不能再出現與關係代(副)詞重疊的成分。例如：
錯句：Is this the train that they took it last Sunday?
分析：該題中that 已經代替先行詞the train 在定語從句中充當及物動詞took 的賓語，故重疊出現的賓語it必須刪去。
總之，突破了以上六道難關，定語從句中的難題便會迎刃而解。
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