"...a set of conditions where practice had been uniformly associated with improved performance.  Significant improvements in performance were realized when individuals were 1) given a task with a well-defined goal, 2) motivated to improve, 3) provided with feedback, and 4) provided with ample opportunities for repetition and gradual refinements of their performance."

Reference:

Anders Ericsson, K. (2008), Deliberate Practice and Acquisition of Expert Performance: A General Overview. Academic Emergency Medicine, 15: 988-994. https://doi.org/10.1111/j.1553-2712.2008.00227.x