The most important thing about the cover letter is to read the job announcement very carefully. Applying for jobs is a job in itself. It takes time and is a lot of work. Write each one of your letters specifically for the job announcement targeted. Letters that are the same for every application with a few changes at the beginning do not stand a chance.
When writing the letter (and later during interviews), try to think of and to include aspects unthought-of by the competition. Before you even start writing, read the job announcement several times and then immerse yourself in the website of the college or university you are applying to. Read everything there is on the program/department’s website as well as any presentation of "mission," "academic vision/objectives," etc. How does the institution identify itself?
When writing your letter, at every chance you get, as many times as possible, quote the institution's/department’s website (and state that you are quoting) and connect it to your profile. Without actually stating it, you want your readers to think of you as the perfect match. Begin several sentences with something like: "I am very impressed by your program in…."; "I notice on your website that…"; "I certainly share your university’s academic vision of…"; etc. Each time, follow this pattern: 1) State what you saw on the website; 2) Immediately relate it to something you did, do, or are trained to do. The idea is to show that this specific program is your priority. Your interest is such that you took the time to study the institution and department/program thoroughly.
Crucial: in your letter, address everything listed as "required" in the job announcement. Do not assume a search committee will scrutinize your CV to uncover on its own every requirement. If the announcement states "Ph.D. in hand by August 2011," specifically state when you will defend your dissertation. If it requires "evidence of teaching excellence and interest at the undergraduate level," have a paragraph starting with these exact words that emphasizes how teaching undergraduates is your passion and that shows evidence of your excellence (a teaching award, a course only assigned to experienced TAs, etc.). Even if the announcement requires candidates to know how to swim, you should address it in the letter! One technique that can be used in cover letters is to put in bold at the beginning of a paragraph or as a heading the announcement’s requirements.
There are two main reasons for making sure you address all requirements: 1) Search committees sometimes must give specific reasons to human resources and affirmative action offices for all the candidates they eliminated from the preliminary interview. Ignoring one of the requirements in your letter may be translated by a search committee as "not qualified for the position"; 2) You show the institution your thorough preparation, motivation, and attention to detail. During my several experiences on search committees, I was often struck by the fact that most candidates never took the time to address all of the requirements or to familiarize themselves with the university and program they were applying to. Most candidates only spoke about themselves. Taking the time to tackle all prerequisites as well as the school/program’s characteristics will certainly impress interviewers.
Moreover, remember that, on average, more than 100 candidates apply for any given position. Consequently, when one considers that, in addition to the cover letter, search committees also have to read CVs, letters of recommendation, writing samples, and teaching portfolios for every candidate, it is in the candidate’s best interest to go straight to the point. The first two paragraphs are the most important of the entire letter. Use this approach when writing the letter: if the reader were only to read the first sentence of each paragraph in your letter, would she/he still know the essentials and would she/he want to read more?
Opinions vary on the length of letters. Personally, I believe that first-time applicants’ cover letters should always be longer than one page but never be longer than two pages. My rationale is as follows: do you want to work for people and a department who believe that graduate students who have not yet begun their career should already have enough to fill four pages of a cover letter? Of course, more experienced applicants should write longer cover letters.
Write your letters jargon-free. Always remember that non-specialists in your field, including administrators, must be able to understand your letter and arguments. If you are authorized to do so, print the first page of your materials on the department’s official letterhead. End the letter with sentences such as:
I would be glad to meet with you for an interview at [your discipline's annual meeting] or elsewhere at your convenience. I am enclosing copies of my CV, and Interfolio Inc. [or other online portfolio service company, or university's career services] is sending you my teaching philosophy, three letters of recommendation, and dissertation abstract. In the meantime, I can be reached at the above home address and phone number (or by email).
I thank you for your consideration and look forward to hearing from you.
Not going to your discipline's meeting is not an option. Meaning, it may seriously hurt your chances if you write that you will not be attending the convention.
Things to consider before sending the dossier: if you have a blog, a Facebook page or any other kind of website material, verify that there is nothing posted there that could kill your job applications. Google yourself as well to make sure that everything showing up is acceptable to you. Also, messages on your home and cell phone voicemails should be sober, clear, and brief (without background music, etc.). Check your voicemail and e-mail every day. If your email address is something like email@example.com or firstname.lastname@example.org, change it!