Human computation allows computer systems to leverage human intelligence in computational processes. While it has primarily been used for tasks that are not time-sensitive, recent systems use crowdsourcing to get on-demand, real-time, and even interactive results. In this paper, we present techniques for building real-time crowdsourcing systems, and then discuss how and when to use them. Our goal is to provide system builders with the tools and insights they need to replicate the success of modern systems in order to further explore this new space.