When you formally ask for letters make sure you have proper etiquette.
1) Set up a meeting as far in advance as possible. Many of the people that you will need letters from probably have assistants, so you should set up this meeting through their assistant. Call or email the assistant, explaining that you will be asking for a letter and that the attending should be expecting this meeting. You can also attach your CV and supporting documents to this email, although you don’t have to if they’re not up to snuff yet. Try to meet toward the end of a rotation with the attending, so they have already had a chance to get to know you but you are still fresh in their memory.
2) Add them as a letter writer on ERAS before the meeting, making sure you have their correct name, degree(s), and title. Then print their unique LOR information sheet and bring it to the meeting. This document contains a unique number for uploading your letter, plus all necessary instructions.
3) When you meet, bring paper copies of your CV, an unofficial transcript, evaluations from relevant third year rotations, and your statement of purpose (even if it's a rough draft). You will give these to your letter writer to help them get to know you.
4) If possible, dress up for the meeting. If you're in surgery, like me, scrubs are fine—just make sure to go through the formality of apologizing for being in scrubs. Make sure you look neat and clean.
5) Prepare for a short interview. They will ask you how you know you want to do that specialty, what your career goals are, etc. Some of my letter writers also asked me questions like my greatest strengths and weaknesses.
6) Ask if they feel they can write you a STRONG letter of recommendation.
7) Say thank you!
Now the tricky part: getting them to write your letter. One of my attendings uploaded her letter to ERAS the day after we met. Another attending took about 6 weeks. He is extremely busy and had a bunch of traveling to do, so I certainly didn’t take it personally, but I did start to get pretty nervous.
To handle the latter situation, you need to be assertive and persistent but never demanding. You should become best friends with your attending's assistant and email him/her weekly. But NEVER be rude to the assistant. NEVER!
Never forget that you aren't entitled to a letter. Your attending is doing you a favor, so all of your communications should have an undertone of humility. I usually emailed the assistant something like, "Hi so-and-so! How are you doing? I'm so sorry to bother you again, but I wondered if Dr. XYZ will have time to finish my letter this week? I appreciate anything you can do to help me get the letter in by September 15th. Thanks so much!" And make sure you thank the assistant when the letter does finally get uploaded.
And if it starts getting close to the deadline, line up a backup letter writer in case they don't come through.