There are any number of ways to arrange seating. You'll want to experiment and solicit suggestions from students. For example, if you want to encourage discussion, place desks or chairs in a circle or horseshoe. If you plan to lecture, arrange the furniture so that all students can easily see you without straining. Ask your students to comment upon present arrangements and on what would be useful for them.
Good environments are frequently flexible ones.
Feel free to have students move their chairs several times during a class. For example, you might have them move into a circle for discussion, into small groups for in-depth exploration of a topic, and back to rows for your lecture. If you plan to have students work in groups but your assigned room has fixed chairs, you may have to be especially creative in grouping students. Asking students in a given row to stand, face students in the row behind, and pair off, is one way to manage the situation. In some newer and remodeled buildings, classrooms have dry marker boards instead of the more traditional chalk.