句子是由词或短语按语法规则组成，表达一个完整意思的语言单位。好的英语句子应该是结构意思正确完整，连贯流畅，言简意赅。但是如果一篇文章中所有的句子都是结构单一(以主语开头，采用"主-谓-宾"或"主-谓-表"的结构)、长短均等的话，句子写得再好，文章也是单调呆板，缺乏生气。要克服这种句式"单一"现象，可以通过变换句子开头以及句式两种手段。
一、句子开头多样化
写作时最常见的是用名词或代词构成的主语作为句子的开头。除了主语外，句子中还有以下几种成分可以作为句子的开头。
1.以同位语作为句子的开头。试比较下列两个句子：
A. Xiao Wang, our monitor，will attend the meeting.
B. Our monitor, Xiao Wang, will attend the meeting.
句A以主语Xiao Wang开头，句B以同位语Our monitor开头。
2.以单个修饰语作为句子的开头。
这个修饰语可以是形容词、分词或副词。试比较下面几组句子：
A. She is young and ambitious, she works hard to get the job.
B. Young and ambitious, she works hard to get the job.
句A以主语She开头，句B以形容词短语Young and ambitious开头。
C. The girl entered the room gracefully.
D. Gracefully, the girl entered the room.
句C以主语The girl开头，句D以副词Gracefully开头。
E. The students reached the top of the mountain exhausted.
F. Exhausted, the students reached the top of the mountain.
句E以主语The students开头，句F以过去分词Exhausted开头。
3.以短语修饰语作为句子的开头。
短语修饰语可以是介词短语、不定式短语、分词短语以及独立主格结构。试比较下列各组句子：
A. A beautiful girl stood in front of me.
B. In front of me stood a beautiful girl.
句A以主语A beautiful girl开头，句B以介词短语In front of开头。
C. The students worked hard to pass the exam.
D. To pass the exam, the students worked hard.
句C以主语The students开头，句D以不定式短语To pass the exam开头。
E. He was confused about the problem and went to ask for his teacher.
F. Confused about the problem, he went to ask for his teacher.
句E以主语He开头，句F以过去分词短语Confused about开头。
G. You may go home after you finish your homework.
H. Your homework finished, you may go home.