well u can try this thing called the swish method. for a while shoot some free throws, try and shoot them all the same, on the ones that go in swish, say swish as they go in. keep doing that for a week or so, but make sure u shoot them the same every time. then, practice free throws, but say swish just before u shoot the ball.
it uses muscle memory and helps u make ur shots. the record holder for free throws created this method, and he is 80 years old. he made a few thousand free throws in a row using this method, before taking his afternoon nap
