Despite their idiosyncrasies, motor and cognitive learning and endurance sports training have in common that they involve repeated practice. While considerable research has been devoted to the effect of practice on performance, little is known about optimal practice strategies. In this paper, the author models the practice process for both skill acquisition and retention and optimize its profile to maximize performance on a predefined date. For skill acquisition, he finds that the optimal process involves multiple phases of practice increase and decrease, yielding U-shaped effort consistent with the principle of distributing practice, and that the transitions between phases are smoother for skills that are easily forgotten (e.g., cognitive skills) than for those that are easily retained (e.g., continuous motor skills). In particular for the latter, an extended period of rest should precede an ultimate high-intensity stress. For skill retention, the optimal practice strategy consists of cycles of either constant effort (for skills that are easily forgotten) or pulsed effort (for skills that are easily retained) consistent with the principle of alternating stress and rest. His parametric model thus indicates when commonly used high-performance practice strategies are indeed optimal.