Ask my son if practice makes perfect and you will get a resounding "No!". What he will tell you is that practice makes permanent. This is not his own logic, it came from a hockey coach that he has. That coach is right on the money. Practice does not make perfect...it makes permanent. Practice a bad habit over and over, it becomes engrained.
I can tell you that this is true first hand through guitar playing. There are merits to learning guitar on your own, but there are also shortfalls. One of those is if you practice a technique or form long enough in the incorrect way, you will not want to change and it will stunt your ability to be as good as you could be. I have stumbled on that with the use of my pinky finger on my fretting hand. Most average guitar players and some good ones will get away without using their pinky finger much, but the great ones use every tool in the toolbox so to speak. I found out that my pinky has been ignoring the push-up protocol that the others seem to have been doing. Where does that leave me? At the beginning with the pinky finger relearning exactly where it is supposed to be.
Most mornings now, I set a metronome to a specific tempo and run through scales ensuring that I use my pinky finger in the right place. Improvement comes much faster when you can already navigate the course. It would be very similar to tweaking your golf swing. Really just slow down, practice the technique very slowly and deliberately, then get up to tempo...and try not to curse.
I actually enjoy the practice aspect. I can quite literally sit and practice the same little lick, scale, chord progression, whatever...for hours. The key to it I find is that if I start to put in any garbage reps, then I stop and take a short break then come back to it. You see, I also had a coach that told me the same thing in principle so it isn't a new idea. Mine said "Garbage in equals Garbage out". Basically, if you put in garbage reps, you will get garbage results. It also works when you talk about nutrition come to think of it!
So learn from my mistake here newbies. If you try to pick up a new habit, skill, or technique be patient. Do it right. Practice makes permanent. I knew I should have been in the NHL All Star Game...I just practiced the wrong things!