Once the letter is written, add a line space and use either "Yours faithfully," or "Yours sincerely," before your signature. There are several schools of thoughts as to when it's appropriate to use "faithfully," or "sincerely,".Follow this rule:"Yours faithfully," should be used when the name of the recipient is not known (so, in a letter with an introduction of "Dear Sir/Madam:").
A winning cover letter generally consist of three parts which amount up to three paragraphs. In the first paragraph, you will detail why you are writing the company. This will provide context to your intentions for writing the company, which is to apply for a new job. Also, try to provide clues as to where you found out about the job posting and what got you interested in applying. The second paragraph serves as the gist of your cover letter. Here is where you explain what you can offer and what skills matched the job requirement. If you have other skills or achievements, make sure to point them out by referring to your resume. Make sure you can convince them to read your resume.