Design decisions have an impact on societies and the environment. Making the impact of design tangible facilitates the mitigation of its negative consequences. The purpose of this paper is to outline what methods and actions a User Experience (UX) practitioner could use in order to support sustainable development. At Ergosign GmbH, an agency creating digital experiences, we conducted a review of existing guidelines and principles to determine the relevance and usefulness of those frameworks in the User Experience Design (UXD) context. The analysis resulted in the creation of six guiding principles to introduce sustainability concerns into the design process. Additionally, we mapped related UX methods and heuristics to each principle. Each of the six principles, as well as an exemplary method, are described in detail in this article. A first practical evaluation of the principles suggests that assessing impact and identifying preventive actions is possible at all stages of the design process. Furthermore, there is no strict correlation of a principle with a particular project phase. While an early analysis generates a more holistic action plan, a later assessment provides more concrete advice. Both approaches can deliver notable improvements in the reduction of resource usage.