The first thing you should do is meet with the individual and have a brainstorming session. Get a good idea of the exact purpose of the letter and who the recipients and ultimate decision makers will be. This will help you understand the tone and style you need to employ when writing the reference letter and it will also allow you to know the pertinent information required to be included in the specific situation, as well as “what to leave out.”
Your brainstorming session should be quite extensive. You and the person you are writing the reference letter for cannot afford to make a mistake or say the wrong or inappropriate thing. Ask questions about their goals and aspirations. You need to know what they are specifically trying to accomplish so that you can then direct your comments specifically to those goals.
Ask the person provide you with a list of their major accomplishments, the organizations they belong to, and any other relevant information. It may surprise you to see how much that person has done outside of your personal contact with them. This will also help you get a more accurate picture of the individual so that you can truly write the best reference letter on their behalf.
Obtain a copy of their resume and keep this information nearby while writing your reference letter for them. Remember, however, that you should only vouch for what you know from your own personal experience with the individual.
Ask whether there are specific skills, topics, accomplishments, issues, etc., that he or she wishes to be said or included in the letter, and, likewise, whether there are any specific things that should be left entirely out of the letter!
Ask them exactly when the reference letter is due, and make sure that you have adequate time to write the letter in order to have it completed by the agreed-upon deadline. Make every effort to honor the deadline.