The hunt for the most effective machine learning model is hard enough with a modest dataset, and much more so as our data grow! As we search for the optimal combination of features, algorithm, and hyperparameters, we often use tools like histograms, heatmaps, embeddings, and other plots to make our processes more informed and effective. However, large, high-dimensional datasets can prove particularly challenging. In this talk, we'll explore a suite of visual diagnostics, investigate their strengths and weaknesses in face of increasingly big data, and consider how we can steer the machine learning process, not only purposefully but at scale!