So when should you use a cover letter? Only as part of a limited, targeted campaign to reach specific employers. Take the time to research and understand a company before committing yourself on paper or email as a prospective employee. If you have no idea what the company does, do not just submit your resume and cover letter in the blind hope of making a match. If you are not willing to invest time and energy to find out whether a match is possible, why would you expect me as the Hiring Manager to do so?
A successful cover letter should be specific and personal. Each letter should refer to a specific person at a specific company and provide a specific next step that you will be taking in the process. If you wait for them to call you, your odds of contact decrease dramatically. It usually requires a proactive response on your part to move the process forward to the next level. The "squeaky wheel theory" (i.e., the one that squeaks the loudest gets the grease) is alive and well in job search. If you make the effort to contact me, I will respond to you. If you passively wait for your phone to ring, do not expect me to call. If you wait for your resume and cover letter to magically produce results, you will likely find yourself buried underneath the data mountain of other resumes. So you need to be the one who stands out.
The cover letter should cover two important points: (1) what your product can do for your customer (the company), and (2) what your customer will need to do to buy your product. If that sounds like marketing mumbo-jumbo, consider that many marketing people miss those simple points. They spend time telling about their "great" product features, when they really should be concentrating on telling how it will benefit the customer.
If you have no idea how you can benefit that customer, then you may be wasting everyone's time (including your own) in even attempting a reasonable job search. You will most certainly fail any interview. Go back to square one and start over. Know your specific career objective and how your background and experience will benefit potential employers. That is your personal value proposition.
Ask any astute marketing person the following question: "What is your company's competitive advantage in the marketplace?" If that person is good, you will get a quick and ready answer.
You should also have a ready answer to the very same question. If you are just another player in the already very crowded entry level job market, you will not be noticed. You need to fully understand and be able to articulate your personal value proposition.
If you are not sure what differentiates you from the rest of the market, find out! Research your background and make note of the areas where you excel. And make that your number one focus in writing the cover letter.
A basic formula for cover letters is as follows:
That's it! For an example of this format, refer to the sample cover letter that follows. But remember—what is right for one person can sound canned or contrived for the next. Take the time to write a basic cover letter structure you feel comfortable with, then customize it to the specific needs of the specific customer (or at least the industry).