We have all heard this before "practice makes perfect" however this is very wrong! 

PERFECT PRACTICE MAKES PERFECT if you are to practice a shooting form that is incorrect, you will NEVER get better. practice the forms your coaches and trainers teach you. Do not change the form from what was taught to you. 

Practice over and over again and your muscles will remember the form so when you get tired and the muscles get weak you will succeed in what your doing. For example, shooting a freethrow in overtime.