I've found that a good way to get my students to engage in the class is to keep them guessing what I'll do next. Sometimes I'll walk up and down the rows or call on a student seemingly at random. I may assign a surprise in-class project, tell a story or a joke, or act out a scenario. The most common technique I use is the discussion model; rather than lecture I start a discussion to get the class involved. This method does make it difficult to stay on subject at times, but I've found that the student involvement that discussions generate more than makes up for this.