最简单你就可以直接写dear.,
然後看对象是谁 .是妈妈就是"mum/ mami/mother.. " 老师就"teacher/MissX/ Mra.."之类
然後就是"how are you " (问好)
1）开头语
① I am very glad to hear from you.
很高兴收到你的来信。
② Thank you for your letter.
谢谢你的来信。
③ I was very pleased ( happy ) to receive your letter of February 6, 2001 …
很高兴收到你2001年2月6日的来信…。
④ Your letter of February 6, 2001 has been received.
你2001年2月6日的来信收到了。
⑤ It is a pleasure for me to get your letter.
收到你的来信，真是高兴。
⑥ I'm sorry to have taken so long to answer your last letter.
这么久才给你回信很感歉意。
2）结束语
① I hope to have a letter from you before long.
希望不久能收到你的来信。
② Please write to me soon and tell me all about yourself.
请快点给我来信，并谈谈你的情况。
③ Give my best wishes to you.
呈以最好的祝愿。
④ Wishing your business ever successful！
祝你事业有成！
⑤ Hope you are healthy.
祝你健康。
如同汉语信一样，英文信的结尾也常写有"祝好"、"盼来信"、"代向……问好"之类的话，我们称之
为"结束语"
参考资料：http://wenku.baidu.com/view/1ba93b2acfc789eb172dc8af.html