Interest in the instructional application of virtual worlds, such as "Second Life" (SL), has grown substantially. However, little information is available about effective instructional activities using virtual worlds. This case study illustrates lessons learned from a pilot integrating SL into a two-semester English course at a large southwestern US university. A building activity was implemented in the first semester, and based on qualitative and quantitative formative evaluation results and additional planning, the instructional activity for the second semester was modified. These changes substantially enhanced students' learning experiences. Eight general and five discussion/debate-specific best practices discussed for implementing SL in college-level courses include capitalising on social interactions and establishing a clear connection of activities with learning objectives. This study demonstrates the importance of combining careful instructional design with ongoing assessment when implementing emerging technologies. It also indicates that course learning goals and students' needs should be considered first and foremost when adopting new technologies for instruction. (Contains 3 tables and 4 figures.)