Familiarize yourself with the position. Get a copy of the job description, if you can, and talk to the person you will recommend. If you know the intended recipient of the letter, ask them about the position as well. The more you know about the position, the better you will be able to tailor your letter to suit the needs of both parties.
How important are letters of recommendation? Letters of recommendation are required for almost every graduate school application and are a very important part of the application process. Usually grades and test scores factor in most heavily; however, your letters of recommendation could be the deciding factor in the admission process.