Greetings!
If you are supposed to write it as a letter to the boss, that should give you your opening:
Dear Mr. Boss:
I am writing to express my interest in the job and acquaint you with the reasons I feel I am the best candidate for the position. The job of [insert job title] requires [list some things, like good leadership skills, determination, attention to detail, etc.] My experience in [your present or previous position] has given me valuable experience and required development of these skills.
I hope this will get you started! Just continue to talk about the skills, experience and personal traits for the job.
Thanks,
Sarah, EssayForum.com
Sarah, EssayForum.com