Network monitoring and management require accurate statistics of a variety of flow-level metrics such as flow sizes, top- flows, and number of flows. Arguably, the current best technique to measure these metrics is sketches. While a significant amount of work has already been done on sketching techniques, there is still a lot of room for improvement because the accuracy of existing sketches varies with changing characteristics of network traffic. In this paper, we propose the idea of using machine learning to improve the accuracy of sketches, and propose a generic machine learning framework to reduce the dependence of accuracy of sketches on network traffic characteristics. We further present three case studies, where we applied our machine learning framework on sketches for measuring three flow-level network metrics, namely flow sizes, top- flows, and number of flows. We implemented and extensively evaluated this framework for these three metrics using both real-world and synthetic traffic traces. To the best of our knowledge, this is the first work that uses machine learning to reduce the dependence of sketching techniques on the characteristics of network traffic. We have released all our traces and implementation codes at Github.