Read the "Criteria for Application" page on the Dell Scholars website. The page explains the details for the readiness program and other requirements. You must be a United States citizen, and you must plan to enter a bachelor's degree program at an accredited institution.
The applications are graded on financial need, but also on some subjective categories. In 2011, the site said the application was evaluated on the student's individual determination to succeed, the ability to explain personal hardships and how the student overcame them, and "self motivation in completing challenging coursework." Dell says it is looking for how well a student has prepared herself for college instead of a "laundry list of activities and club involvement."
Complete the application online at dellscholars.org. The application must be received between November and mid-January of the applicant's senior year. The semifinalists are announced in February, and the winners are announced in April.