寫信的原則（Writing Principles）已從原來的3（Conciseness, Clearness, Courtesy）發展到目前的7個"Ｃ"：

Completeness, Clearness, Concreteness, Conciseness, Correctness, Courtesy,Consideration)

實例

Dear Sirs,

　　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 License. As soon as we are informed of the number of the Export License we will open the L/C by cable.

Copper Wire

大意：
　　關于你們四月九日涵，我們高興地接受你們第8/070/02B號報盤單所報100噸紫色銅絲。請著手辦理申請出口許可證。　一經接到出口許可證號碼的通知，當即電開信用證。

要求書信的"完整"，　理由有三：
１．一封完整的書信比一封不完整的書信，有更大的可能性帶來預期的效果；

２．一封完整的書信，有助于建立和表達友善關系；

３．一封完整的書信，可以避免由于遺漏重要情況（情報）所導致的訴訟（Lawsuit）；

有時，某些不顯眼的書信或文件，由于所提供的情況完整而又生動有力（Complete and Effective）而成為極為重要的文件。一封信寫得是否完整，建議用五個"Ｗ"來檢驗，即：Who, What, Where, When 及Why(包括How)。例如:在定貨的信中，必須明確說明"需要什么商品(What you want)、何時需要(When you need the goods) 、貨物發到何地何人收(to Whom and Where the goods to be sent) 、如何付款(How payment will be made) 如對對方的要求作出否定的答復時（如不能報盤，不能理賠等）應說明理由，為什么(Why)

Clearness(清楚)

（一）．避免使用可能產生不同理解或意義不明確的詞匯〈例一〉As to the steamers sailing from Hongkong to San Francisco, we have bimonthly direct services. (從香港到舊金山有直達船，)但是bimonthly 究竟是一個月兩次即半月一次呢，還是兩個月一次？不明確。因此，最好清楚明白地說明"一個月兩次"還是"兩個月一次"：

（a）We have two direct sailings every month from Hongkong to San Francisco.（每月兩次直達船）（b）We have semimonthly direct sailing from Hongkong to San Francisco.（每半月一次直達船）（c）We have a direct sailing from Hongkong to San Francisco every two month.（每兩個月一次直達船）

（二）注意修飾詞的位置，有時修飾詞的位置不同，會導致不同的含意如：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. 以上兩句中的""修飾的內容不同：a) 你們要求我們盡快做些什么。b) 請盡快告訴我們。所以a) 可譯成"請告你們要我們為此盡快做些什么"； b) 可譯為"請盡快告知，你們要我們為此事做些什么"。

（三）注意代名詞，關系代詞和先行詞的關系按照英語習慣，句子中的代名詞和關系代詞一般是指離得最近的名詞，因此要特別注意，以免引起誤解或不清楚。例句：不好：They informed Messrs.John & Smith that they would receive an answer in a few days. 較好：They informed Messrs. John & Smith that latter would receive an answer in a few days.

(四)注意前后一致和緊湊，連貫不一致：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.