Assuming that this is about writing a covering letter to support a job application, it is important to get it right from the start. Starting a letter by addressing it to 'Dear Sir or Madam' instantly gives the impression that the applicant cannot be bothered. The principal has a name, and if the applicant really cared he would find that name. A simple phone call to the school will reveal that name and instantly raise the letter in ranking among other applications.
Boring cliches like 'I would like to apply' will have the principal reaching for a pillow. A headline like 'Experienced Teacher Seeks Immediate Employment' will make him sit up and take note.
Doing a little research will reveal if the school intends to solve a problem, such as raising graduation rates, for instance. Instead of listing previous experiences in a boring fashion, they can then be used to let the principal feel the applicant is just the right person for the job at hand. It should be clear that the applicant will use his experience to his full potential, because he enjoys a challenge.
Most people assume that they may be contacted. This common mistake can be avoided by letting the principal know exactly where and how to contact the applicant, and that the applicant expects to be contacted. Something like 'You may contact me on, enter contact details, to arrange an interview shortly' should do the trick just nicely.
A PS at the end of a letter seems to act like a magnet on readers. Adding a PS expressing a desire to discuss the job and adding a time limit, say a week, before the applicant will check back works a treat.
