Hanon exercises are reknown, albeit controversially for allowing you to build full finger independence and agility. While they work great for this, they are often critiqued for taking too long to learn, reducing practice time spent learning actual pieces, and also being potentially dangerous for the hands / wrists if practiced with poor technique or with too much force. I actually began learning them after already spraining my right wrist severely from overpractice of high end pieces without having done any technical exercises. I have actually found these exercises when played correctly have fully fixed my wrist and undone the sprain, though I had stopped playing already for 13 years as I had thought my wrist problem was more severe until recently when I had it X rayed and all the bones are fine. It took me about 2 months to get through the first 31 exercises, which are the main notable ones for building full finger independence and evenness, and now my pinkies feel just as strong and agile as my thumb's except for not being opposable. The pain was still coming back in-between practice but with less and less severity, but I don't plan to quit so hopefully it might eventually go away fully. Learning these exercises also now makes learning any piano piece vastly easier as I no longer struggle to learn the fingering and can now read, play and learn Joplin ragtimes very quickly and with zero strain (my favourite genre). In less than a month, I can already slowly play the first three sections of Gladiolus Rag both hands together and am close to finishing and mastering the piece, whereas a decade or so ago it took me almost a year to learn just one piece!