A subject line specifying the topic of the letter, if included, comes between the salutation and the body of the letter. The introductory word Subject may be used, but is not essential. The terms Re and In re should be reserved for legal correspondence.
The subject line is usually placed between the salutation and the body of the letter (with a blank line in between).
Here are six steps to write a letter of instruction: Create a header. Before you write the content of the letter, create a header at the top left-hand corner of the document. Address the reader. Explain the project or task. List each step. Conclude your letter. Revise the document.