Political scientists have recently conducted hundreds of randomized field experiments to examine the effectiveness of various mobilization methods for increasing voter turnout. Given the high degree of internal and external validity, the empirical findings of these studies have a potential to significantly impact the practice of get-out-the-vote (GOTV) campaigns in the real world. In this paper, we offer an essential and yet missing methodological tool that allows GOTV campaign planners to best utilize the results of such field experiments. In particular, we show how to derive the optimal GOTV campaign strategy from field experiments. Our nonparametric method is applicable to partisan or nonpartisan campaigns as well as campaigns with multiple mobilization methods of the same or different costs. We evaluate the effectiveness of the proposed method using three existing field experiments. In multiple cases, we find that the resulting optimal campaign strategy is more than twice as cost-effective as a naive strategy.