To apply insights from complexity science to the real-world requires practitioners to judge which tools and methods are appropriate to use in some situations and when, where and how to apply them. This involves characterisation of complex situations; guidance on the type of adaptiveness needed; and understanding of the principles driving change. To that end, this chapter first provides a model of practice, and a framework for judging appropriateness of tools based on that model (with three examples of the framework in use). The chapter then offers a critique of two sets of example tools: examining the applicability of autonomous agents and multi-agent systems to a range of situations; and explaining how to employ multi-modal, multi-level influence networks to bring about ongoing change. Finally, the chapter presents a list of principles of practice, drawn from experience in the field, to be used to inform real-world decision- and policymaking.