1.注意介词的选择，要根据从句来确定，不能受主句影响！
This is the room in which I live.
先行词room在从句中要加上介词in作地点状语，也就是作in的宾语。
从句还原应该是I live in the room.
此句也可以转换成：This is the room which I live in.
I have paid for the house in which he lived.
2.注意此句不能用for which，分析此句时，先确定先行词the house，其次确定the house或which在从句中要加介词in作状语。
不能受主句中the house前介词for的影响。
The man (to whom you talked just now) will chair the meeting tomorrow.
= The man (whom/who you talked to just now) will chair the meeting tomorrow.
He told me the tickets are hard to buy, in which case you’d better buy right now.
(which作case的定语)
He told me the tickets are hard to buy, and you’d better buy right now in that case.
The books, some of which he has read, are very interesting. 表示整体与部分关系
The books are very interesting and he has read some of the book.
The students, most of whom have seen the movie, are from our class.
The students are from our class and most of them have seen the movie.
He spent 2 hours there, during which time he slept.
He spent 2 hours there and he slept during that time.
The boss in whose department Mr. King worked had a heart attack.
The boss had a heart attack. Mr. King worked in his department.
3.注意在固定短语中介词不能提前，比如：care for, call on, put off, listen to, look for, look after等，如果把它们拆开，那么这些短语就失去了原来的含意。
The old man whom I am looking after is better.
