At Sabers athletics, we prefer the phrase "practice makes permanent." The way you practice leads to the way you usually perform on the court or field. If you always practice with proper technique and a positive attitude, you will play with proper technique and a positive attitude, Good practice leads to good play. On the flip side, poor practice can lead to poor play.
It's tough for volunteer coaches whose main job is full-time teaching to have enough time and energy and expertise to prepare and run "perfect" practices. There are hundreds of books and online articles about how to improve your practices. Here is one good article with 15 tips for a better practice. It's worth the quick read.
As always, go Sabers!