Mass communication is a process where generic messages are transmitted to broad audiences. Targeted communication instead customizes its message for a specific demographic. The thinking is that people in that demographic are more likely to appreciate your service than others because it in some way targets needs and desires specific to them. Tailored communication is even more specific - it individualizes messages for specific receivers. In the age of social media and Big Data, it is increasingly possible to profile people in this way.
Marketers are heavily reliant on data to individualize their promotions and advertisements to specific audience members. Take the story of Target discovering a girl's pregnancy before her father did. The store is so effective at understanding customers based on their past purchasing habits that it can identify pregnant women and send them promotions booklets full of items they're statistically more likely to buy. This approach has obvious advantages and disadvantages for the public interest. On one hand, it benefits people to receive advertisements for things they might actually want, rather than for items with mass appeal that they have no interest in. This turns ads from spam to potentially helpful. On the other hand, there are privacy issues here, as most people are uncomfortable with the idea of retailers having access to their personal information.
Tailoring makes other kinds of communication more effective, as well. Tailored health communication has had modest success influencing cancer screening, smoking, dieting habits, and others. Some of these attempts have integrated ideas from the literature on narrative persuasion.
Rimer and Kreuter suggest that tailored health communication can increase motivation to process health information in four ways: (1) by matching content to the individual's needs and preferences, (2) by framing message content in a context desirable to the individual, (3) by designing messages in such a way that catches the individual's attention, and (4) by customizing outbound promotions strategies according to the individual's desired channels, type, and frequency of messages. To make this more intuitive, think of the process of sending job applications. If you send a generic email to 30 companies, you're far less likely to hear back than if you tailor each email to the individual company. Each company is looking for something different, so you benefit yourself by catering to their individual needs.
Consider the extended elaboration likelihood model of persuasion. People scrutinize messages harder when those messages are considered personally relevant to them. One study showed significantly greater cognitive activity in individuals receiving tailored brochures rather than a standard brochure or even a standard brochure designed to look like the tailored brochure. Greater processing was associated with increased intentions to change behaviours. Many other studies have confirmed the effectiveness of tailored health communication, but there also exist situations in which good-fitting, non-tailored communications are at least as successful as tailored communications.
Several theoretical models of behaviour change have been applied to tailored health communication. Most notably, the transtheoretical model of behaviour change holds that people exist in one of six stages of change: precontemplation, contemplation, preparation, action, maintenance, and termination. Behaviour change communicators are considered to be more effective if they tailor their communications according to each individual's stage of change.
Behaviour change models may guide health communication but they do not dictate how to optimize specific messages in such a way that their impact is maximal. For that, you still need to know the psychology of persuasion and to read research done on marketing, advertising, and communications.