Write a short list of people who are well qualified to recommend you. Choose someone who not only knows you well, but holds an advanced degree in your field (preferably the degree that you intend to pursue) and has supervised and evaluated your work in that field. Admission readers often think professors with whom you have taken upper-division courses are best qualified to recommend you.
Meet with each person on your list individually. Ask if they are willing to write a strong recommendation letter for you. Consider ruling a potential reference out if you sense any hesitance or if they decline. Ask early to allow each recommendation writer plenty of time to supply a letter for you.
Provide each recommendation writer with a brief portfolio. Include a cover letter that shows your contact information, the schools to which you are applying and the due dates of each program. Fill out and include any recommendation forms required by the programs. Give the recommendation writer a copy of your statement of purpose, transcript, resume/curriculum vitae and examples of your best work if you have not worked with them recently.
Send a note, either by e-mail or by post, thanking each reference personally. Wait two weeks to a month, if the due dates allow, before sending the thank-you notes. A thank-you also acts as a gentle reminder to write and submit your letter if its still unfinished.