As its creator explains, Just-In-Time Teaching (JiTT) is a "teaching and learning strategy based on the interaction between web-based study assignments and an active learner classroom. Students respond electronically to carefully constructed web-based assignments which are due shortly before class, and the instructor reads the student submissions "just-in-time" to adjust the classroom lesson to suit the students' needs. Thus, the heart of JiTT is the "feedback loop" formed by the students' outside-of-class preparation that fundamentally affects what happens during the subsequent in-class time together."
In addition to the main JiTT website, these sources provide more information and ideas about how to use this active learning method:
Vanderbilt's Center for Teaching has created a Teaching Guide.
A Sampler of JiTT assignments in various disciplines.
Carlton College provides this guide, with links to further resources.
Watch this video case study of the impact of Just-in-Time teaching in a Geology class.