
If you are interested in requesting a letter of recommendation from me (or anyone else), you will want to read the following carefully in order to ensure that you get a letter and that it's a good one.
Keep in mind that not everyone is the right choice to write a letter for you: The best letters will come from professors that know you, have worked with you, and with whom you've ideally interacted outside the confines of a classroom. Sometimes, your letter-writers may indicate that the letter they would write for you would not be the best it could be, simply because they probably don't know you well enough to do a really good job. It means nothing beyond just that: it just means that your interactions with this letter-writer have not been extensive enough, and that you should probably seek a letter from someone that knows you a little bit better. This is a good thing: you'll get a much better letter from someone that is more familiar with your accomplishments.
The best time to make a request for a letter of recommendation from a professor is during their office hours, although sending an email a couple of days in advance letting them know that you'll drop-in would help as well.
Writing a good letter of recommendation takes a good deal of time, and time is hard to find in a hectic schedule. Make sure to leave plenty of time before any deadlines the letter must meet: request a letter at least two to four weeks before its deadline, and make sure to let your letter-writer know what the deadline actually is.
Make sure you handle and provide to your letter-writer all the details that are needed to ensure that the letter gets to the right place in time. You'll need to clearly inform them of who the recipient is and what the preferred delivery method and letter format are. If the letter must be mailed to its recipient, make sure to provide your letter-writer with a pre-addressed and stamped envelope.
You really don't want a generic letter, fit for any and all situations for which you may need a letter of recommendation. What you really want is a targeted letter that is custom-written for a specific opportunity that you are applying for.
You'll want to provide your letter-writer with a detailed description of what you need the letter of recommendation for, and any special criteria or concerns that are particularly important. That way, the letter can be tightly focused and, therfore, much more helpful to your purpose.
You really want to make the task easy for your letter-writers, and the best way to do this is to provide them with a lot of information:
The best letters are those that are honest and straightforward, and include a realistic perspective that acknowledges challenges and shortcomings. Therefore, you want your letter-writer to feel comfortable being honest. To ensure this, understand that letters of recommendation are confidential. If you have a choice between keeping letters confidential or not, always choose to keep them confidential.