英语短信作文的写作要点可以概括为以下几点：

明确目的：

在开始写作之前，明确短信的目的。是为了表达情感、传递信息还是请求帮助等。

使用适当的称呼：

根据收信人的身份和关系，选择合适的称呼，如“亲爱的”、“尊敬的”等。

简洁明了：

短信内容应简洁明了，避免冗长和复杂的句子结构。尽量使用简单词汇和短句来表达意思。

保持礼貌：

无论是表达感谢、道歉还是其他情感，都应保持礼貌和尊重。

注意格式：

短信的格式应与正式信件相似，包括称呼、正文和落款。日期通常放在信件的开头或结尾。

审阅和修改：

在发送之前，仔细审阅短信，检查语法、拼写和标点符号错误，并进行必要的修改。

示例1：感谢

Dear [Recipient's Name],

I hope this message finds you well. I wanted to take a moment to express my sincere gratitude for your help. Your support has meant a lot to me, and I am truly grateful.

Thank you again for everything.

Best regards,

[Your Name]

示例2：邀请

Hi [Recipient's Name],

I hope you're doing well. I'm writing to invite you to join us for a small gathering this weekend. It'll be a great chance to catch up and have some fun.

Please let me know if you can make it.

Looking forward to hearing from you.

Best,

[Your Name]

示例3：询问信息

Dear [Recipient's Name],

I hope this message finds you well. I'm writing to ask for some information about the upcoming English competition. Could you please provide me with the details regarding the event？

Thank you for your time and assistance.

Best regards,

[Your Name]

通过遵循这些要点，你可以撰写出清晰、简洁且富有礼貌的英语短信作文。