This research investigates how conversational user interfaces (CUIs) can be designed to support everyday food services, making them more robust, effective, and productive. While CUIs are increasingly integrated into daily life, their usability remains inconsistent, and best practices are still evolving. The study explores the intersection of service design, artificial intelligence, and entrepreneurship to address these challenges. Through a series of action research projects, this work examines how CUIs impact users, merchants, and service ecosystems. It demonstrates how service design research methods can be combined with entrepreneurial modes of practice to generate knowledge within live organisational contexts. The findings show that effective conversational service design requires moving beyond static representations and interface-level optimisation, towards dynamic tools, practices, and learning mechanisms that account for human behaviour, organisational constraints, and system evolution over time. The primary contribution of this thesis is the articulation of a set of empirically grounded design principles for AI-enabled conversational services. These principles are brought together under the framing of Conversational Service Design (CSD), which extends service design thinking into the conversational AI domain by supporting reflective, adaptive, and organisation-aware service design practice.