Scholarship agencies will often times ask for you to provide letters of recommendation. There are several tips on how to get this done, and done well.
You should ask people who know your professional and educational abilities:
As soon as possible! Give your letter writer at least 3 weeks of notice to get the letter to you. You can always plan ahead and ask teachers for letters after you finish their class. If you do need a letter quickly, call the person (do not email), and let them know exactly what you need and when. If you ask for a letter last minute it is very important to formally thank them.
You will normally ask your author to write a one to two paragraph letter, stating how the author knows you and examples of your good work. Feel free to give your author a little help by filling out the Letter of Recommendation Request Form[pdf]. This gives you a chance to clearly state what you would like your author to touch on, and when you would like the letter to be done.
Letters of recommendation are important to your scholarship application not only because it confirms your skills and strengths, but it also shows that you stay connected with the community of people around you. Staying connected with people who can help you (and you can help them) is a skill that can make you successful in the work place. The support of others can say a lot about your potential.
It is important that you formally thank the person who wrote your letter. Either send them a thank you card, or email them. Even if you don't get the scholarship, send them a thank you note, saying "although I didn't get the scholarship I applied for, your help has meant a lot to me...".