It depends on the teacher, but normally a trial lesson includes a brief interview and then an introductory lesson. Be sure to take your instrument with you! If you have taken lessons before, it would be a good idea to take any music you’re working on, as well as a list of repertoire you’ve worked on in the past. The idea of a first lesson is to assess what level you are and what your goals are, so that your teacher can devise a plan for your lessons.