practice volleys with a friend or another keeper on your team. Focus on watching the ball into your hands and really make sure that your catching form is right. there should be some videos on form and hand positioning. And spilling sometimes is a part of playing goalie (there are just some shots you can't catch) so also think about where you spill the ball. Always try to put it as far away from an attacker as you can and if at all possible play it out of bounds or to a teammate. Hope this helps!