【正确答案】Dear Lily,
I am very glad to hear that you want to learn something about English letter writing in order to find a good job after the coming graduation.
Actually, there are quite many good books in this respect. However, to you, I highly recommend Mr. Shouhua Qi's The New Century Guide to Practical English Communication, for it is especially practical and comprehensive. This book covers various forms of communication in written English such as business letters, resumes and social correspondence.
What's more, the author gives a detailed and incisive explanation on these writings. If you can make a careful study on this book, I am convinced that your skills of letter writing will be greatly improved.
Warmest regards.