Keep in mind: You're asking a very busy person for a favor, one that will require extra (possibly unpaid) hours out of his or her life. You'll want to streamline this process and make it as easy as possible. Remember the recency effect. Asking for a letter is the last impression you'll make before the letter is written. If you come across as sloppy, disorganized and inconsiderate, it will be hard to write an LOR heralding your boundless empathy, stellar professionalism and impeccable attention to detail.

How to get your letter.

• Do good work as a student or trainee. You aren't entitled to a LOR, you earn it because you impressed someone with your work.
• Decide on your final list of sites.
• Gather all the site information you'll need:
  • Name and address of the site
  • Name and title of the training director
  • A general idea of the position ("adolescent inpatient clerkship")
  • Whether they want letters mailed or emailed
• Get your CV together.
• Write a paragraph about what you want from your next placement ("I'm focusing on college counseling centers because I plan to enter that field later in my career. I'm looking for more training in theory....etc.").
• Print envelopes addressed to the sites wanting paper letters, even if you're going to hand-deliver the letters or send them all in a package. Include stamps if the writers are mailing them.
• A few weeks to a month before the deadline, start asking current and past supervisors if they would have any problem writing a good LOR for you. Email is fine.
• If they say no, you may want to politely ask why, for your own information, but don't press them for a letter - now you don't want a letter from them.
• If they say yes, thank them and quickly email them:
  • the names, addresses, training directors and general info from your sites, 
  • who gets letters and who gets emails (drop off envelopes if necessary)
  • a copy of your CV,
  • your paragraph, 
  • whether you need letters mailed or if you'll pick them up,
  • the date you need them completed,
  • your heartfelt gratitude.

• If they haven't completed the letters 10 days before they're due, send a gentle reminder (you can actually call it a "gentle reminder") asking if everything is in order and ask when you can pick them up. Start thinking of your backup letter writer.
• If you still don't have their letters five days before the due date, panic. Beg your Plan B to write a letter, tell them your sob story and offer to wash their car. Fortunately, this doesn't happen very often.
• Don't ask to read the letter. Don't fabricate a fake site just so you can open and read it. Don't use steam to loosen the seal, read the letter, then re-seal it. It's bad form, along the lines of asking your great aunt how much she's leaving you in her will. Some profs will send you a copy of what they wrote to soothe your curious, affirmation-seeking mind, others wont. Try to trust that if they agreed to write you a letter it's going to be pretty good, and leave it at that.
• Thank them again after you collect all the materials.
• When you find out where you were placed, write to let them know where and thank them for their help. Yes, it's gratitude overkill. But no professor ever says "That student is too damn grateful!"

I know this sounds like a lot of work on your part. But you never know, you may need to ask for another letter next year or 10 years from now, and this will help you get a positive response now and in the future. And someday before too long you'll be an LOR writer, paying it forward. You'll wonder where you put this article, wishing you had given it to your supervisees/students first.