Get the Job.
A covering letter provides a great opportunity to highlight key attributes and your experience directly relevant to the position you are applying for. You should try to keep the letter to one page and your introduction brief.
Your resume should have a formal tone, while your letter allows you to let your personality and enthusiasm shine through.
Maintain a standard formal business letter format but consider the position that you are applying for. If it is in a sector such as financial services a straightforward formal style will be expected. However, if it's for say, the advertising industry, a more creative approach may be appropriate.
Mention the job you're applying for and explain why you are right for it. Use the following paragraphs as an opportunity to develop these points and expand on your experience and aptitude for the job. You should finish your letter positively and confidently by giving your contact details or stating when you intend to contact them.