Having your class write a one page biographical sketch can be a very effective way for you to learn several things about them quickly. Students may balk at the idea of having to write an essay about themselves on the first day of class, but letting them know that the essay will not be graded and that it will help you be a more effective teacher for them will usually remove any apprehension about writing. The most effective way to learn as much about your students as possible from these essays is to establish a predetermined list of things you would like to know and write them on the board. Asking your students to tell you about their family, their school experience and intended major can be helpful. It can also be advantageous to have them write one paragraph on their expectations for the course and what they may know about the subject already.
Rather than have your students write about themselves, you may want to have them write about other students in the class. An effective activity for learning about your students and for getting them acquainted with one another is to pair them off at the beginning of the first class to have them interview one another. It may be necessary to establish a short list of four to five questions to get them started. You can then require that they ask a certain number of additional questions beyond the ones that you require. As a take-home assignment, require that students take their interview questions and answers home to write a biographical essay about the person they interviewed. The intention is to have them read their essays at the next class session, so you may not wish to let them know this ahead of time; some students may be apprehensive about reading aloud in class and may skip class as a result. As an incentive, you can offer the students a small extra-credit incentive, but only if they turn in the essay at the next class session.
Another effective strategy for students to get to know one another is to play game of "truth or lie?" This can also be a way for you, as an instructor, to learn several things about your students. Have each student write down a list of four or five items about themselves. If using five items, have students write down four truthful things about themselves that they consider interesting. Make the fifth item a lie. Have them read the list aloud in class ask the class to vote on which of the five items is not the truth. Once the votes are in, have the student reveal which item is not the truth.