For a general letter of recommendation, focus on generalized qualifications for the job category for which your coworker is applying. If writing a letter for a specific job, refer to the job posting or description to note specific job skills that you can include in your letter, suggests About.com.
Start your letter by introducing yourself and noting how long you have known the candidate, states Scribendi.com. Highlight the candidate's skills and relevant experience as these relate to the position. It's also useful to discuss your coworker's personality traits and overall disposition. Include how the candidate works alongside others and how she will benefit the company.
Format the letter by including your name, contact information and date at the top of the letter. Ask your coworker if there is a specific person to whom the letter should be addressed, or address it generally to a human resources representative. Keep the letter at no more than one page long.
Create a list of your coworker's strengths to assist you with creating your letter of recommendation. Give a specific example or two in order to paint a clear picture of your coworker's strengths. Upon closing the letter, let the recruiter know if you would enjoy working with the candidate in the future.