Advice on Letters of Recommendation
Another issue is whether letter writers should attempt to address weaknesses in your application. For example, if you received a low Quantitative Graduate Record Exam score due to a family crisis immediately before the test date, your letter writer might mention this and argue that the "A" you received in Statistics is a better measure of your quantitative skill. This strategy can be very helpful in some situations, but it is also a double-edged sword that can draw attention to weaknesses in your application. Thus, you should discuss the pro's and con's of this approach with your letter writer before adopting such a strategy -- each situation is unique, and there is no single best way to proceed.
Once you have 3-4 letter writers and a game plan for what you'd like the letters to say, there are two more things you can do to increase your chances of success: