Subjects are usually volunteers from Psychology classes.
To recruit subjects go to see the instructor at least several days before the scheduled class. Some instructors might want you to come at the beginning of class, some at the end. You will want to prepare a description of your experiment for the class. The students will want to know the general topic, how long it will take, and if possible, what they have to do. This is a bit difficult, because you don't want to tell them the exact conditions, but you still want to make it interesting.