How to be a better goalkeeper?

In 1 on 1 situations, there is very little you can do. By that point, your defense is no help at all and it's all up to you. You can increase your odds of saving a goal by rushing the attacker and making your arms wide and taking up as much space as possible. As for the low shots, do some agility exercises on your own or something. Maybe you could have a friend take some low shots and just practice working on your reflexes.