Research the place to which you are applying. You will want to find out exactly the type of person they want, including that person's training, experience and personality traits. For every supporting statement you write that corresponds with your Curriculum Vitae, you will want to personalize it to fit the place to which you're sending the statement.
Open the piece with a paragraph introducing yourself. Start your statement by explaining your interest in the position offered, including why the opportunity excites you. Tell the person any interesting aspects of the place in which you hope to work.
Discuss your credentials and training, including any particular courses you've taken and the subjects in which you specialize. If you're applying to a teaching post, cover your experience in the classroom.
Talk about any research projects of which you've been a part, as well as any written work, such as a senior thesis that will help to provide a well-rounded picture of yourself as a scholar.
Explain your strengths in working with others. If you usually take on a leadership position, be sure to discuss it. If you help to keep co-workers or peers on track, let the potential employers know.
Briefly describe your role in any relevant volunteer or extracurricular activities that lend themselves to helping you get the position.
Move on to discussing your work philosophy and the type of work environment you wish to have. Remember that you want the supporting statement to reflect your confidence, and by asserting yourself as a candidate who only wants the very best for themselves, you will look all the more attractive to potential employers.
End your statement by concluding in a confident manner the exact reason why you should receive the position. State that because of your extensive experience and work ethic, you are an excellent candidate for the job.