Practice the way you wish to perform. When you arrive at a game the hope is that you can play effortlessly. The essence of this is that your mind and body already know exactly what to do. You can step onto the field and not have to worry or over think anything. You might need to adjust strategy or change course, but things should move rather smoothly.
To achieve this goal though one must give their all at practice. Anytime you show up to practice you must give it everything you’ve got. Work together with your teammates and coaches. Study your opponents. Prepare for every match. If you hold back at practice you will inevitably end up holding back during the match.
As a goalie coach I have had several goalies tell me they don’t go all out during practice because they don’t want to hurt their teammates. That being said, they also complain to me that their teammates and head coaches go too hard during practice and put them in dangerous situations. I would agree with my goalies that you never want to injure your teammates, but at the same time, you want to stay safe. Your teammates are giving everything they have at practice so that when they get into a game they will be ready to go. Your also need to acknowledge that and go all out. This will do two things, 1) help prepare you for your matches and 2) help keep you safe during practice.
Holding back in practice can also lead to injury during matches. When your body isn’t properly prepared you will be more likely to get hurt doing something that should come natural.