Somewhere between practicing everyday for years and shooting 3 arrows and heading into the woods lies how much practice you will need. Only you can determine that. It will go a lot easier if you have a knowledgable person tune your bow. From there you want to practice like you will hunt. Tree, ground, sitting, standing etc. Shooting is only 1 variable to the equation. The other things more important than shooting are discipline and remaining calm. Shoot only YOUR shots. Which for a beginner should be 20 yds or less, and broadside or slight quartering away aiming for the ribcage. Don't force your shots and don't panic. Having hunted before should help you there.

Good luck.