The purpose of a letter of applicationis to help the applicant obtain the job he is interested in. It should state clearly what position the applicant wants, and should tell what his abilities are and what he has to offer. It should provide a quick, clear picture of the applicant's qualifications, accomplishment and aims. It should present the applicant to possible employees in the best light.
A well-written letter of application, however, does not necesarily guarantee a position; but it does insure consideration and a better chance of an interview. The applicant cannot hope to get his whole story into his letter, but he should cover enough ground to intrigue the prospective employer and make the employer willing to meet him, speak to him, and find out more about him. It takes more than a good letter to land a job; instead, it takes ability, specific experience, and good character. But the letter may open the door for the applicant, and give him the chance to "sell" himself.
A letter of application should be simple, human, personal and brief without omitting any essential or pertinent facts. The applicant is well advised not to write a dull, stereotyped letter of application. What he should do is to make the letter interesting. Generalities should be avoided in it, that is, it should be specific. The letter should be typed if possible. When the applicant can neither type his letter, nor has it typed by someone else, he should write it out very neatly and legibly in case the letter is discarded for its illegibility.
1. To explain where the applicant has got the information about the vacancy. For example, he can learn it from his friends, or in the advertisement, or in some papers, or he just wants to try his luck.
SAMPLE: Having noticed the enclosed advertisement in this morning's South China Daily, I wish to apply for the position of sale's manager.
2. To Present personal information. This part should be a description of the applicants age, sex, education, working experience and specialty. It is in this section that the applicant presents his advantages or qualifications for the position. Details are encouraged, but the applicant should bear it in mind that exaggration or false descriptions are not allowed in the letter.
SAMPLE: I am 21 years of age. After graduating from high school, I took a two-year business course in Foshan Commercial School, studying both bookkeeping and typewriting. I now wish to enter an office where the work requires great individual responsibility and judgment, and where there is an opportunity for achievements.
3. To claim your referees（推荐人）.The applicant is well advised to enclose in the letter the names as well as the addresses of two or three referees after he has got their permission. Referees are of great importance for obtaining a job, for they are the best and most persuasive support for the condidate's potential, merits and strength.
SAMPLE: I have obtained permission to give the names of the following persons as references: Professor Song Xieli, Director, English Department, Haitai University; Mr. Wang Qing, Manager, Human Resource Department, Chinese Import & Export Corporation.
4. To inquire the chance of an interview.
SAMPLE: I should welcome a personal interview at your convenience.
A、 I am not only competent to install a filing system that will fulfill the needs of your corporation,but also well qualified to operate it efficiently.(我自信不仅可以设置一套能满足贵公司需求的档案分类系统，而且可以有效地进行操作。)在此句中使用了not only……but also，competent 和well qualified 等词语，表现得太自信，有夜郎自大之嫌，故不可取。
B、I think that I should probably make a good accountant for your factory.（我想我可能成为贵厂的一名好会计员）。此句中的情态动词should和副词probably 所表达的语气都欠肯定，而make（成为）一词也缺乏自信，整句话显得语气太弱，有自卑感，因此亦不可取。
C、I am confident that my experience and references will show you that I can fulfil the particular requirements of your secretarial position (我相信我的经验和证明人可以向您表明，我能够符合贵单位秘书一职的特定需要。)此句中的confident 一词语气肯定，给人一种自信感，而will show 和I can 也无自大之嫌，因而此句用得恰到好处，有特殊风格。
相关阅读： 英文求职信写作步骤 英文求职信的写法