There are many books available on this process. I make several available to students. I read them successful essays from past students who have given me permission to share them with future classes. As we begin this assignment, we discuss the application process in general, financial aid opportunities, etc. I've collected over the years with students.
Students prepare a brag sheet of their activities, awards, and employment.
I discuss with students how they should approach teachers and other adults when asking for letters of recommendation. The earlier the better, but I do warn students to remind their recommenders politely until they are sure letters have been mailed. We discuss the waiver they may be asked to sign regarding confidentiality of the letter. I strongly recommend that students waive their rights to see the letter as I feel admissions officers will place more weight on a confidential letter. I tell students that they should choose the people they ask carefully, for both their ability and willingness to write a good letter.