一、Courtesy 礼貌
语言要有礼且谦虚，及时地回信也是礼貌的表现。
例如：
We have received with many thanks your letter of 20 May, and we take the pleasure of sending you our latest catalog. We wish to draw your attention to a special offer
which we have made in it.
You will be particularly interested in a special offer on page 5 of the latest catalog enclosed, which you requested in your letter of 20 May.
二、Consideration 体谅
写信时要处处从对方的角度去考虑有什么需求，而不是从自身出发，语气上更尊重对方。
例如：
“You earn 2 percent discount when you pay cash. We will send you the brochure next month. ”就比 “We allow 2 percent discount for cash payment. We won’t be able to send you the brochure this month.” 要好。
三、Completeness 完整
一封商业信函应概况了各项必需的事项，如邀请信应说明时间、地点等，确忌寄出含糊不清的信件。
四、Clarity 清楚
意思表达明确，要注意：
(一)避免用词错误：
例如：As to the steamers sailing from Hong Kong to San Francisco, we have bimonthly direct services.
此处bimonthly有歧义：可以是twice a month 或者once two month.故读信者就迷惑了，可以改写为：
1.We have two direct sailings every month from Hong Kong to San Francisco.
2.We have semimonthly direct sailing from Hong Kong to San Francisco.
3.We have a direct sailing from Hong Kong to San Francisco.
(二)注意词语所放的位置：
例如：
1. We shall be able to supply 10 cases of the item only.
2. We shall be able to supply 10 cases only of the item.
前者则有两种商品以上的含义。
(三)注意句子的结构：
例如：
1.We sent you 5 samples yesterday of the goods which you requested in your letter of May 20 by air.
2.We sent you, by air, 5 samples of the goods which you requested in your letter of May 20.
