Send in the final applications well before the deadline to leave time for corrections or to locate missing items of the application. The application deadlines for Ph.D. programs are usually from early to late January. This makes it easier on the schools but it is more work for the applicant. Then check off each completed item.
Letters of recommendation are the main sources of such information.
Request that they write the letters and briefly discuss your interests and plans. Faculty members who know you from small classes and as advisors in research projects can write the most valuable letters. Do not bother with letters from professionally irrelevant people such as family friends, clergy, and prominent business or political figures. Discuss your plans with the letter writer. The more information you provide, the easier it will be to write a letter that specifically addresses your interests and plans and best supports your application.