成考英语写信主要取决于信件的类型。以下是几种常见信件类型的格式：

1. 询问信：这种信件通常以"Dear ______,"开头，然后是"I am _________ (自我介绍)."接着是"I am writing to see if it is possible for..."，最后以"Thank you for your time and consideration."或"I look forward to your early reply."结束。

2. 请求信：在请求信中，你需要以"Dear___________,"开始，然后是"I am writing to formally request to___________ (请求的内容)."最后以"Thank you for your understanding and assistance."或"I appreciate your help."结束。

3. 道歉信：道歉信通常以"Dear ____,"开头，然后是"I am truly sorry that__________ (道歉的原因)."接下来是"Once again, I apologize for any inconvenience caused."或"I hope you can forgive me."结束。

4. 建议信：在建议信中，你需要先介绍自己，然后明确指出你的建议。例如："You have asked me for my advice with regard to _______（问题），"接下来是"In my opinion, the best course of action would be to___________ (提出的建议)."最后以"I hope this helps."或"I wish you the best of luck."结束。

5. 求职信：求职信应以"Dear Sir or Madam,"开头，然后是"I am writing to apply for the position of___________."接下来描述你自己的能力和经验，最后以"Thank you for considering my application."或"I look forward to hearing from you soon."结束。

6. 邀请信：邀请信通常以"Dear________,"开头，然后是介绍自己和写这封信的目的，如："I am writing to invite you to___________ (活动详情)."最后以"I hope you can make it."或"Looking forward to seeing you there."结束。