Writing a strong cover letter is tricky business in any situation, but if you are trying to land a job at a company you used to work for, you may need to take extra care in how you word the letter. The most important thing to consider before writing your cover letter is why you left your old job, and why you now wish to return. Regardless of whether you left under positive or negative circumstances, you can write a cover letter that will impress the employer and land you an interview for the second time.
Write down your thoughts on why you left the job, why you want to reapply and what new skills you have developed in your experience since leaving the company. These thoughts do not need to be in your letter, but serve to help you organise in your mind what you are going to say.
Start a document with your header (name and contact information) at the top, followed by the name of the recipient, the company name and contact information. Open your letter with a formal greeting, addressing the recipient by name (i.e., "Dear Mr. Brown").
Write an introductory paragraph. Explain in a few sentences your current work situation in a positive light, and how you feel that returning to the company plays an important role in your goals for your career.
Write the middle paragraph. Avoid summarising points made in your resume; not only will the recipient have your resume, but the company already knows much of your experience. Instead, focus on what the company needs from the employee who will fulfil this position, and what new skills you have acquired during your absence from the company that qualify you as the best candidate for the job. If relevant, make connections between your past successes with the company and what you plan on doing for them in the future.
Write the closing paragraph, indicating you would like to pursue an interview. Thank the recipient for considering you, and type a closing and your name.
Your cover letter should be single spaced, with a space in between paragraphs, and should fit onto one page.