It is in your interest to do everything you can to assure yourself the best possible letters of recommendation. You should have both a long-term and a short-term strategy for getting excellent letters of recommendation.
Your long-term strategy should have two components. First, you should do everything you can do to be the best student you can be. A careful, detailed, and honest letter of recommendation will portray you as being as good as you are -- not better than you are. Second, you should find a mentor or two and cultivate your relationship. One of the natural advantages you have by being at Cornell is the opportunity to take several classes from a single professor who teaches in an area of interest to you. Look for opportunities to increase your contact with your mentor(s). Choose a mentor for your academic advisor. Consider an independent study or honors thesis under a mentor's supervision. Give your mentor(s) the opportunity to know you well and to see you at your best. And, of course, ask your mentor(s) for letters of recommendation.
The short-term strategy is to help your recommenders write great letters. That means recognizing that a good letter of recommendation is a major task for the recommender. I routinely spend between two and four hours writing an initial letter of recommendation for a student. The time required to prepare subsequent letters is minimal, so unless there is some compelling reason not to do so, ask the same two or three people to write all your letters. Because letter writing is a major task and faculty schedules are crowded, it is critical that you request letters of recommendation long before you need them. I recommend six week's notice. Finally, you should provide your recommenders with a well-organized portfolio containing all the information a recommender might need to write the best possible letter for you. For years I have been asking students to prepare such a portfolio for me when they want letters of recommendation.
The materials I need to write the best possible letter are listed below. I insist on having these materials. It is a waste of my time to write a weak letter of recommendation that won't have any impact. It is a waste of my time to write on behalf of a student who doesn't think the letter of recommendation is important enough to warrant assisting in its preparation. Naturally I think that all your recommenders deserve the same consideration whether they ask for it or not. – Taken from Craig Allin, Professor of Politics, Cornell College. For the full letter from Professor Allin visit here.
Your portfolio should include:
1) a list of the schools to which you will apply
2) the application due date for each school
3) the specific degree, specific major, and the name of the department to which you are applying for each school, e.g. the MA in Applied Anthropology in the Department of Anthropology, the combined J.D & PhD in Law and Anthropology in the Department of Social Sciences, etc. because schools, department names and programs vary a lot
4) a copy of your completed personal statement
5) your current unofficial transcript
6) a resume
7) Any recommendation or waiver forms supplied to you by the institution seeking the recommendation. Type (or print with extreme neatness) the portion you are supposed to complete and sign the form in the appropriate place
8) A legal size envelope for each recommendation with the appropriate address neatly typed. Check carefully to determine which institutions want recommendations mailed directly and which want them included in your application package. The envelope should be stamped if the recommendation is to be mailed directly to the institution requesting it. Unstamped envelopes should be addressed to you for return in campus mail. Be sure to type the name of the institution on the outside of the envelope so you will know where to send it.
9) When asking faculty or staff members for letters of recommendation, the Berry Career Institute advises that you give at least 4-6 weeks notice before the actual school deadline.