We all know it.  We practice and we get better.  Not necessarily better at what we want to do better.  Just better at what we practice.

Doing something requires brain/muscle/nerve communication (both sending and receiving).  When we practice something over and over, our brains and muscles 'learn' the pattern in a process called 'motor learning.'  After a while, the movement(s) get processed on auto-pilot.  We start the thought and then the pattern takes over.

This sounds great, doesn't it?  I'm all for automation!  But, automation is only good when it is correct.  

One of the first things I can remember (this is going back a long way, now) when I started playing sports was being told the importance of repetitions. I don't really recall much about the quality of those repetitions, more along the lines of, "c'mon, keep it up, another lap, grind it out, don't give up..."  Definitely more of a focus on quantity than quality.  And, the familiar phrase, "Practice makes perfect."  

Now that I'm older and wiser, I now know that the rule would be better stated as, "Practice makes permanent."  Perfect has the connotation that it is good and doesn't need any more practice or adjustments.  Permanent means, "uh, oh, if this is permanent, it had better be right!"

Individual attention, instruction and guidance go a long way to making sure that your practice is 'GOOD' practice so that your motor learning will be what you want it to be and you will get the results you are looking for from all your hard work.