Dear American Friends,
Hello!
The trade between China and America is becoming frequent,the GDP of China has come the third in the world last year.By the time goes,the communications between us must be more frequent,so let's build the good friendship between us,let's make the world better,shall we?
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Best Wishes
Yours
XXX
这样开头比较亲切,然后把自己要说的主要内容在第一段开门见山,具体内容再分段叙述,最后加祝福语,署名,就可以了