Char Booth, a 2008 Library Journal Mover & Shaker, writes about four components of "instructional literacy"–reflective practice, educational theory, teaching technologies, and instructional design–and provides practical strategies for effective library instruction.
A Couple of Definitions:
The discipline of instructional design offers a series of complementary design practices that enable the identification of needs and the design of best solutions. These solutions are most often instructional in nature, but they can also be informational or activity-oriented—focusing on improved processes, tools, and conditions for human activity. ID is based on a systematic methodology for assessing needs and developing goals, analyzing the content domain and target population, and designing, developing, and evaluating solutions.
From A Survey of Instructional Development Models (3rd edition)," Gustafson & Branch (1997)
Four major activities define Instructional Development:
L. Dee Fink is highly regarded for his approach to instructional design. While his model is aimed primarily at course design, a step in his process—Initial Design Phase: Building Strong Primary Components—is helpful for designing effective one-shot library sessions. Check out pp. 2-23 in his freely available resource "A Self-Directed Guide to Designing Courses for Significant Learning," or his book for a more thorough discussion of his "integrated course design" model. A very succinct summary of Fink's model is available from the IDEA Center: IDEA Paper No. 42.