1. 宾语从句与表语从句需要与主句的时态配合：主句是现在时范畴，从句可以使用所需要的任何时态；主句是过去时范畴，从句一般也是过去时范畴。例如：
I think that he will come/came to your help. (will come是现在是范畴；came是过去时范畴，都对。)
I thought that he would come/had come to your help. (would come与had come 都是过去时范畴，都对。)
2. 经常使用it充当形式宾语和形式主语，避免句子“头重脚轻”。例如：
I found it too hard for him to finish the work in 2 days. (形式宾语)
It is believed that the earth was flat at that time in Europe. (形式主语)
