写信的原则(Writing Principles)已从原来的3个“C”(Conciseness, Clearness, Courtesy)发展到目前的7个“C”：Completeness, Clearness, Concreteness,Conciseness, Correctness, Courtesy, Consideration
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 Licence. As soon as we are informed of the number of the Export Licence we will open the L/C by cable.
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。
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。
“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)
