Letters of Reference
Students periodically need to request letters from professors for various reasons - applications to graduate/professional schools, support letters for academic offices, admittance to degree programs, etc. Depending on the intended outcome, the letter can require varying amounts of expertise and input from a professor. For instance, I have had students ask for letters of support as they try to get one course substituted for another, while other students have needed recommendation letters for their applications for prestigious awards or programs. Obviously, depending on the target audience, a referee needs to emphasize different aspects of a student's background. Thus, a student can greatly assist the professor in writing a strong letter if the student provides meaningful information to the professor. First a few general recommendations on this front and then some specific thoughts and instructions on requesting a letters from me.
General thoughts
Consider carefully who you want to ask for a letter of recommendation. Letters are very important components of most applications...sure those transcripts, exam scores and GPAs are important, but often it is hard to differentiate between applicants based solely on these less-revealing yardsticks. Letters written by real people can reveal volumes.

The best professors to write letters on your behalf are those who know your work and abilities well and can speak to them both positively and candidly. Consider those words carefully before you request a letter from a professor. If you did not perform the best in a certain professor's class (lower than a "B" I would say) it can be hard for the professor to really glow about you in a letter, and that is what you NEED to have in a letter. Furthermore, if you had a professor for only one class several semesters ago, and you had little interaction with the professor - what can you really expect them to write about you? The reason decision-making bodies (like graduate admissions committees) ask for letters of recommendation is to gain insight about a candidate from responsible adjudicators who know the applicant. If your professor is not that person, you should probably try to find someone better to write that letter.

Once you have decided to ask a professor for a letter, do so tactfully and professionally. Stopping a professor while passing in the hallway probably isn't the right way to do it. For starters, it is probably best to send an email and ask for a 15-minute meeting. Then at the meeting, present your request and then tell them to consider it and ask if they can get back to you with a decision within a week - that gives the professor time to consider the request and whether they could write the letter easily or not. Professors may be able to answer you on the spot, but they may also need time to assess things a bit.

Once a professor has agreed to write a letter for you, get together a detailed but concise information packet for her or him. Different professors might have different needs, but in general it would be wise to include: 1) a request letter that notes deadlines, addresses and potential highlights for the professor to cover, 2) a copy of your curriculum vitae and/or transcript, 3) copies of any necessary forms for the professor to fill out, and 4) a copy of the signed letter  indicating your willingness to waive your right to see the materials submitted by the referee.

Hard though it may be to believe, professors are generally quite busy people with many different jobs to perform. Although you see your professor in front of the lecture hall or lab for only a few hours a week, when not before your eyes they are likely doing research with students, working on committees, writing reports, editing journal articles, writing grants, wrestling with administrators and hurtling through myriad of other tasks. By providing detailed, precise and concise information to your professors, you can better assure your request does not get lost in a pile of goo on their desk.
Specific thoughts
If you are going to request a letter of reference from me (Alec Lindsay, alindsay@nmu.edu) , here are the things I will need in my hands at least two weeks prior to the application deadline:
  1. A written request from you that notes deadlines, addresses and the destination for your application. Also, you should mention highlights from your academic career that might be meaningful for me to touch upon in my letter. There is no guarantee I will mention them, but it doesn't hurt to remind me of things, does it?
  2. A copy of your curriculum vitae, and possibly your transcript. I do not necessarily need your transcript, but if you would like to share the fact that you aced organic chemistry and African history, you can send your transcript to me as well.
  3. Copies of any forms that I may need to fill out and return with my letter.
  4. A copy of the signed statement indicating you waive your right to see the recommendation letter. This is usually something included with application packets when you get them, and they affect the ability of any referee to speak candidly and openly.

Finally, you shouldn't need to include any envelopes or stamps for me to write a letter - we can cover that for you almost more easily than if you give me a stamped and addressed envelope.
The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.
                        -Bertrand Russell, Philosopher, mathematician, and writer (1872-1970)