Do not type the letter heading or inside address. Type the title of the course, which exam it is, and the date. For example: "English 3232: Renaissance Literature. Exam No. 1, Feb. 2, 2012."
Create a heading that says "Instructions" and type the instructions for completing the exam. For instance: "Instructions: Write your name at the top of this letter. Then, complete each section by writing the correct response under each question. If you need additional space to answer each question, continue your answer on a separate piece of paper. Use pencil so that you may erase mistakes. Mail this letter exam back to me at: Dr. Laura Momboko, Department of Mathematics, Big State University, 111 Big State Blvd, Houston, TX 72525. Your exam must be postmarked by Feb. 16, 2012."
If your exam will be proctored by another university or a testing center, explain that process as well so the student will know where to go and how to sign up for a time at the testing site. (see ref 1)
Create another heading for the exam questions, and type each question. Make sure that your questions are appropriately numbered and that your questions are clear. Remember that your students can't ask you immediately if they have problems understanding your questions, so have someone read them over to check for errors or areas that are unclear before you send them out. Provide enough space under each question for the student to write her response.