Translating current principles of language learning into effective classroom practice requires a nuanced understanding of the cognitive and social factors that shape how learners engage in instructional activity. In this paper, we identify four principles that represent a current theoretical consensus in the field, which we hope will guide practitioners as they assess their work: (1) "All language use is purposeful, but not all language use is meaningful"; (2) "we learn by doing"; (3) "metalinguistic knowledge (still) matters"; and (4) "social contexts co-construct development." We then critique a common assumption that teachers can seamlessly implement pedagogical recommendations from available professional development opportunities and materials. Although the methods and techniques proposed through professional development may provide examples for implementation, only a deep personal understanding of principles can inform how they are most effectively realized in any local context. It is therefore the responsibility of teacher education and professional development providers to better articulate justifications for their recommendations and explore flexible adaptations in their application. It is also incumbent on researchers and theorists to better understand the realities of practitioners so that the principles they espouse will translate more readily into meaningful recommendations for practice.