写信的原则（Writing Principles）已从原来的3（Conciseness, Clearness, Courtesy）发展到目前的７个Ｃ：
Completeness, Clearness, Concreteness, Conciseness, Correctness, Courtesy,Consideration)
实例
Dear Sirs,
Copper Wire
With reference to your letter of April 9, we are pleased to accept your offer of 100 tons of Copper Wire as per your Offer Sheet No.8/070/02B. Please go ahead and apply for your Export Licence. As soon as we are informed of the number of the Export Licence we will open the L/C by cable.
(信的本文汉译)：
关于你们四月九日涵，我们高兴地接受你们第８／０７０／０２Ｂ号报盘单所报１００吨紫色铜丝。请着手办理申请出口许可证。 一经接到出口许可证号码的通知，当即电开信用证。
要求书信的完整， 理由有三：
１． 一封完整的书信比一封不完整的书信，有更大的可能性带来预期的效果；
２． 一封完整的书信，有助于建立和表达友善关系；
３． 一封完整的书信，可以避免由于遗漏重要情况（情报）所导致的诉讼（Lawsuit）；
４． 有时，某些不显眼的书信或文件，由于所提供的情况完整而又生动有力（Complete and Effective）而成为极为重要的文件。 一封信写得是否完整，建议用五个Ｗ来检验，既： Who, What, Where, When 及Why(包括How)
例如:在定货的信中，必须明确说明 需要什么商品(What you want)
何时需要 (When you need the goods)
货物发到何地何人收(to Whom and Where the goods to be sent)
如何付款(How payment will be mande) 如对对方的要求作出否定的答复时（如不能报盘，不能理赔等）应说明理由
为什么(Why)
Clearness(清楚)
（一）．避免使用可能产生不同理解或意义不明确的词汇 〈例一〉 As to the steamers sailing from Hongkong to San Francisco, we have bimonthly direct services. (从香港到旧金山有直达船，) 但是bimonthly 究竟是一个月两次即半月一次呢，还是两个月一次？不明确。因此，最好清楚明白地说明一个月两次还是两个月一次： （a） We have two direct sailings every month from Hongkong to San Francisco. （每月两次直达船） （b） We have semimonthly direct sailing from Hongkong to San Francisco. （每半月一次直达船） （c） We have a direct sailing from Hongkong to San Francisco every two month. （每两个月一次直达船）
（二）注意修饰词的位置，有时修饰词的位置不同，会导致不同的含意如： a) Please let us know what you wish us to do about this matter as soon as possible; b) Please let us know as soon as possible what you wish us to do about this matter. 以上两句中的修饰的内容不同： a) 你们要求我们尽快做些什么。 b) 请尽快告诉我们。 所以 a) 可译成请告你们要我们为此尽快做些什么； b) 可译为请尽快告知，你们要我们为此事做些什么。
（三） 注意代名词，关系代词和先行词的关系 按照英语习惯，句子中的代名词和关系代词一般是指离得最近的名词，因此要特别注意，以免引起误解或不清楚。 例句： 不好： They informed Messrs.John Smith that they would receive an answer in a few days. 较好： They informed Messrs. John Smith that latter would receive an answer in a few days.
(四)注意前后一致和紧凑，连贯 不一致：Being a certified public accountant, I am sure you can help us. 一致： Being a certified public accountant, you can surely help us. or; As you are a certified public accountant, I am sure you can help us.
（五）仔细和恰当地分段落（Paragraphing） 商业书信要写得使人一读就明白，因此必须按照内容仔细和恰当的分段落，一般的分段落原则是一个段落一个意思（A paragraph for each point is a good general rule.）. 现举例说明：
Dear Sirs,
It is reported in a domestic newspaper that the Iranian Central Bank has instructed the commercial banks to suspend their business of opening a new letter of credit as from the 3rd May for financial reason of foreign currency. Although it is said that this arrangement would be a temporary one and with establishment of new import policy this emergency arrangement would be lifted, we are much concerned about the outcome of this movement toward restriction of import to Iran and shall be obliged if you will kindly keep us well advised of development of this new arrangement especially in connection with import from France.
Yours faithfully,
以上这封信只有一段，供两句。第一句39字，第二句66句。 读后虽然能基本了解其内容， 但读起来很舒服。信的内容大体有三点：
１． 伊朗中央银行因外汇原因，通知个商业银行从五月三日起停止开立信用证；
２． 这临时措施，新的进口政策一订，这个措施可能取消；
３． 希望对方随时告之有关情况。 按照这三点，适当地分分段落，把信重新改写一下，可能读起来比原来的清楚易懂：
Dear Sirs,
It is reported in a vernacular newspaper that the Iranian Central Bank has instructed the commercial banks to suspend their issuing new Letters of Credit as from the 3rd May because of its decreasing foreign currency funds.
Furthermore it is said that the suspension seems a temporary one and will be released with establishment if a new import policy.
We are much concerned, however, about the outcome of this movement toward restriction of import to Iran. We, therefore, shall be obliged if you will keep us well informed of development of this new state of affairs, especially in connection with imports from France.
Yours faithfully,
Completeness
实例解说：
Cellulose Tape 1/2x 3yds, with plastic dispenser 700 doz./-ditto-but 1/2 x 5 yds, 1,000doz. 这是出口商接到的一份定单中有关商品品名，规格和数量的内容。中文意思是： 纤维素带（幅）宽半英寸，长３码，带塑料包装容器，７００打；同上，但（幅）宽宽半英寸，长５码，１０００打。
主要问题是后半句不清楚。 ditto在这里表示前面提到的商品名称纤维素带，但不能包括带塑料包装容器，因此，幅宽半英寸长５码的纤维素带是否有塑料包装容器没有说清楚，不完整。 所以最好改成： Cellulose Tape 1/2x 3yds, with plastic dispenser 700 doz. Cellulose Tape 1/2 x 5yds，with plastic dispenser 1000 doz. 这样即完正，又清楚明确，不会引起误解。