Video and film especially, due to their very nature, could risk putting the class into a more passive mode. After completing a Preview of the multimedia element, give the students a clear task to do while listening, watching, exploring, etc. You can use the results of such a task as a starting point for Follow-up activities. Nothing can throw off the cadence of your lesson like computer gliches, videos and cassettes not properly cued, video monitors that are not warmed-up, etc. Also, too many technical problems could distract the class from the lesson at hand.
Many instructors set-up multmedia components to their lesson before class begins.
In this way, no teaching time is lost during the transition to multimedia-based activities. Some of the materials in the Professional Development section of the storage cabinets in CZ 248 give excellent hints for using video in creative ways in the classroom.