Understanding the pre-existing social relationships in a setting is vital in health promotion, not only for understanding important people to get 'on side' with an intervention but also for appreciating how the intervention itself might change social structures. Social network analysis is a method for capturing the complexity of social relationships that has not been used widely in health promotion research. We present the results of an application in a high school. We characterize the school in terms of the density of relationships and the centrality of particular staff and teachers. We illustrate how simply being well-known or being nominated by lots of others as a person to turn to (a concept reflected in a person's degree centrality score) is not always the best guide for whom to select as an intervention champion. Indeed, for many interventions, a person's strategic connection to the most marginal people in a community, school or workplace could be the most important criteria (a concept better reflected by a person's betweenness centrality score). Given the ease of survey administration and the high yield in terms of analytic insight, we recommend that social network analysis be used more routinely in health promotion intervention design and evaluation.