Many employers ask prospective employees to provide references, both personal and professional, before hiring. Employers use these references to help determine a prospective employee's character. If asked to write a job reference for a friend, you should aim to give clear, honest insight into the character of the person you're writing a reference for.
Open your letter of reference by briefly introducing yourself and stating that you're writing a letter of reference on behalf of your friend. Reveal how long you have known the person you're writing the reference for.
Use concise sentences to describe the work ethic and moral character of your friend, but don't go overboard with adjectives. A couple of well-chosen adjectives will do. Too many adjectives, no matter how flattering to your friend, will make your letter sound contrived. Be honest and flattering in your letter of reference, but don't sound as if you're trying too hard to make your friend look good.
Give details about any work experience you've had with your friend. If you can add anything regarding his or her timeliness and dedication to finishing a job, be sure to include it. If you have concrete examples, give them without going into too much detail. Aim to keep your letter at around one page and no more than one and a half pages.
Conclude your letter by stating that you recommend your friend for the job and why. Tell the prospective employer why your friend would be a valuable asset to the company. Include your contact information and state that you are available for further questions if need be.