Most people will be asked at some time to write a job reference for a co-worker. If you feel comfortable highlighting a co-worker's qualifications, express it in a letter. Follow the steps on how to write a letter of reference and you'll have your letter written in no time.
Explain how you know the person and how long you have known her when you open the letter. For example, "I have worked side-by-side with Amy on several marketing promotions for the last five years and I believe she is the perfect candidate for this position."
Tell why the person is the perfect candidate for the job with specific examples of her qualifications. Example: "Amy is deadline-oriented. Whenever a project is due, she works overtime or takes work home, so she will meet her deadline. "
Ask the person what some of the traits are the prospective employer is looking for. If she has these qualities, mention them in this section of the letter and again, back up your claims with specific examples. Example: "You are looking for an organised individual for this position and Amy is one of the most organised people I know. She has colour-coded her filing system and can quickly find any file I need."
List your qualifications and why it matters that you wrote this letter. Why should the prospective employer listen to you and your opinion? You have already addressed some of this in the first paragraph when you tell how long you have known this person and how you knew her, but you still want to tell a little of your background here. Add your contact information if you are all right with someone contacting you for follow-up information.
End on a positive and brief note. You can close with something like, "Thank you for taking the time to consider my letter of reference for Amy. As you can see, she is an organised, deadline-oriented, creative marketing manager, who would fit perfectly into your company. "
Don't mention the person's weaknesses. If they are constantly five minutes late, don't put that in the reference letter. But also, you don't want to lie or stretch the truth. Remember, your credibility is also at stake. So, don't write in the job reference that the person is punctual if she is always five minutes late.
Don't get carried away with your background information in the reference letter. One or two sentences about you and why you are fit to write this letter is plenty.