Whackm makes a good point and it's one I rarely see brought up. Essentially, practice does not make perfect, Perfect Practice Makes Perfect.

I've seen a lot of people who go to the range and launch arrows. When a bad shot happens they don't know why it happened, they aren't analyzing what they do. These people are doomed to reach a level of competancy and basically just stay there.
The individual who pays attention to what he is doing will know that a bad shot was because of release, or too tight a grip on the bow, etc. and then make a conscious effort to learn and not repeat that error. This person will rise in skill.

Guy