How nice to hear from you again.
Let me tell you something about the activity.
I’m glad to have received your letter of Apr. 9th.
I’m pleased to hear that you’re coming to China for a visit.
I’m writing to thank you for your help during my stay in America.
With best wishes.
I’m looking forward to your reply.
I’d appreciate it if you could reply earlier.
英文书信一般由六部分组成。即:信头(Heading)、信内地址(Inside Address),称呼(Salutation),正文(Body of Letter)、结束语(Complimentary Close)、署名(Signature),有时在书信后面还有附言(Postscript)、附件(Enclosure),这得视具体情况而定。