Couple of tips for getting reference letters.
1) Always give your reference plenty of time. Don't rush the reference letter.
2) Ask the person about reference letter first, then send him the forms
Below is a sample letter to request reference letter.
"Dear Professor John, I was a student in your Computer Network class in 2009. You may remember that I wrote my final paper on Speeding Up TCP Connection. I am currently applying to be a software engineer for company XYZ, and am wondering if you would feel comfortable writing a reference for me?"
If the person says yes, then send the forms to him. As difficult as it may be to hear, you want to give someone the opportunity to say no to serving as a reference for you. You need a warm-hearted recommendation, not a plain reference letter just for the sake of it.
3) Always provide your reference a copy of the job description and a current copy of your resume. No one can know everything about you, and it's very helpful to put things in perspective.
4) Ask your reference to address specific skills and competencies in his letter. Dividing responsibilities in references is a very smart strategy. One reference can address not only your great personality, but also your event-planning skills. Another can address your super personality but highlight your counseling and disciplining skills.
5) Always, always thank your reference-writer. The writer took time to compose a letter for you - you should at the very least return the favor. Similarly, keep your reference writer in the loop -- did you get the job? When you do, write another thank-you note.