The Internet of things (IoT) has been identified as a significant contributor to increasing Information and Communication Technology (ICT) energy consumption in the future. Carefully designing interactions between client applications and systems in the IoT may positively impact energy saving. For this purpose, IoT middleware, the underlying software that manages those interactions, should consider energy efficiency strategies a first-class concern. Furthermore, adding an energy-awareness capability to the middleware could significantly contribute to deepening developers' understanding of energy consumption by applications and helping them minimize the energy demand. In this paper, we propose energy-efficiency strategies and integrate them into an IoT middleware. We also offer a model to calculate the energy consumption of the interactions between an IoT consumer application and an IoT system, which the middleware could use to choose the best strategy to constrain the application's energy consumption to a given budget.