What is the best way to make a slightly blurry image a little sharper, while still maintaining some control over the process?

ANS: A  Because Sharpen is have in-cress and Decrees   Ctrl.so u can adjust the level of sharpen or blur 

if we want to change again and again the settings we need to first of all convert the image into the smart object then after we can change the settings true the sharpen Edges.