Since its publication in 2008, Query/View/Transformation-Relations (QVTr) claims to be the standard model transformation language (MTL) for the declarative specification of model transformations, and has been used as an enabling formalism. In consideration of productivity being a central goal in MDE, it is vital for tools and editors to maximize the usability of their implementing MTL. However, taking into account the current state of the art in tools for QVTr, several shortcomings are revealed. First, the availability of matured tools is sparse, and furthermore, they have been developed with the goal to enable the underlying technology. Their design is not user-centered and, in particular, they lack from a poor level of automation and interactivity. In addition, we identify a lack of support for short feedback cycles, which significantly influences the usability of both the editor and implementing MTL. Finally, we consider the neglection of QVTr's concrete, graphical syntax in state of the art editors as unused potential for an increase in readability and traceability. In the context of this thesis, we shed light on the impact of an increase in interactivity, automation, readability, traceability, the usage of QVTr's graphical syntax, and of short feedback cycles on the usability of QVTr. For this purpose, we propose a theoretical concept comprising techniques to push the modeling process towards a user-centered approach. The underlying key principles of our concept comprise the so called outward modeling style, a suggestion-driven process, interactive graphical model visualizations and the enforcement of conventions. To show the feasibility of our approach, we conduct user experiments in an industrial context at the LieberLieber Software GmbH company in Vienna, using a prototypical implementation.