I am almost always able to write a letter of recommendation for former or current students. Very, very rarely I feel I can't write a letter because I don't know a student well or I couldn't write a positive letter. I will let you know in the extremely unlikely event that this is the case.

If I'm writing letters of recommendation for you, there are a few things you can do that will help me write a better letter and will keep me sane.

• Send me an email for each letter you want me to write. In this email, please clearly indicate the due date for the letter, to whom it should be addressed, and when it is due. If you are applying for grad school, please specify the exact name of the department/program you area applying to. E.g., is it "Department of Art History" or the "Art History Department?" And also specify the exact name of the degree you are seeking.
• If you want to send me multiple letter requests in one single email, that's fine too. Just please separate the requests clearly, and list due dates and such. In a typical year I write 60-70 letters, so it gets to be a lot to keep track of. But once I have the basic info and due date on my to-do list, it won't get lost.
• Send me a copy of your CV or resume. This is helpful since sometimes I comment on other things you've done in addition to taking classes and/or working with me. This is especially important if you're applying after you've been out of school for a few years.
• Please send me a copy of the statement of purpose of application essay. It doesn't have to be a final copy. A rough draft is fine. I'm not going to quote from this or critique it, but it's helpful for me to read it so I can put my letter in context. For example, if you write about how you want to go to grad school so you can save endangered squids, but I write that you are going to grad school to pursue your love of statistics, my letter might not be so effective.
• If there is anything you want me to highlight in my letter, please let me know. Perhaps there are some aspects of your work that you're especially proud of. Or maybe you are worried that a graduate department will need reassuring about some part of your background.
• If the recommendation is a hard-copy letter, there is no need to fill out an envelope. I will write or print the address on a spiffy official COA envelope. You also don't need to give me stamps. I have a budget for those.
• It's really helpful to have at least a week or two lead time to write a letter, especially the first letter of the season. Stuff happens, though, and if you need a letter on shorter notice, I understand.

Writing recommendations takes a little bit of time, but it's part of our job. So you shouldn't hesitate to ask. Also, once I have one letter written for you, writing another letter is quick and easy. Letter writing is one of those favors that is not really repaid, but instead is "paid forward." I had people in the past who wrote letters for me; I am writing letters for you; and someday you will write letters for others.