When you are competing for a place in a graduate program, for a scholarship, or for a job, sometimes -- most of the time, in the case of scholarships and grad school applications -- your letters of recommendation from people who know you and know your work are the deciding factor in whether or not you will succeed.
Here are some hints for improving your chances.
1. Look carefully at what's wanted by the people or the committee the letter will go to. If they ask for a statement of purpose and/or mention specific criteria they want addressed, make sure you actually "fit the profile."
2. Prepare a draft statement of purpose and also prepare a draft of short paragraphs that could honestly describe you.
3. Take your drafts to at least one of the people you want to recommend you, and see if they will help you to make them sound as professional as possible -- and as truthful and accurate as possible. It is a very BAD idea to have spelling and grammar errors or typos in these drafts...
Also bring along anything else relevant -- a copy of your transcript, copies of all the materials the grad school or employer sent you, your resume, etc.
For more hints about getting good letters of recommendation, try some of the following university web pages:
Remember -- no one is required to write you a letter of recommendation, so ask nicely and give them something to work with.