In your first email message remind the Professor who you are. "I am Sam Adams, who took your Spanish 453 class in the Winter of 2009 and Spanish 550 in Spring of 2010." Update the professor on your recent activities. "Since graduating I have been working for the Department of Student Housing at Emporia State University, supervising the RAs." State the purpose of the recommendation and the deadline. Make sure you leave at least two weeks between time of initial request and this deadline.
Once the professor agrees to write for you, provide your resumé and whatever other documentation you are submitting with the application (personal statement, cover letter). I don't retain detailed notes about every student I've ever taught, so I need to take cues from your own intentions.
Make sure that the professor knows you beyond the classroom, or has some insight into your character / personality, etc... How am I supposed to know how well you work with others, whether you are dependable, if I have only academic work to judge you by?
Take no for an answer. If the professor says sh/e doesn't know you / remember you well enough, that means that the recommendation will not help you in any way. If I am the professor who knows you best, but I cannot recommend you, then you are in trouble. You should have cultivated at least a few recommenders over the course of your undergraduat and / or graduate career. By cultivating I mean: (1) Taking more than one course from. (2) Going at least few times a semester for office hours, and (3) not just for assistance or complaint. Let the professor know about your career objectives / interests. Those are the students I will remember and be able to recommend later on. You don't have to be brilliant to do this. One student I supported had less than 3.0 average, but was getting A's from me in the third course she took.
After 10 years, you should not be relying on your undergraduate professors for recommendations. At that point, you will have other, more recent references. If you studied with me for graduate school, then I will continue to support you, but only if we have kept up contact during the intervening years.
I may need you for a recommendation too. I needed student letters for my promotion to full professor and my (failed) bid for Distinguished Professor. I follow these same rules myself. I only asked you for a letter if (1) You took several courses from me. (2) It seemed like you derived benefit from those courses and would have something positive to say.