Communication and commitment
The goalkeeper has a considerable advantage over their teammates: they have the game in front of them. They can also relay valuable information to their teammates, helping them get into position to defend the goal and combat their opponents. Here, we're getting down to one of the most important qualities of a goalkeeper: good communication. They shouldn't be afraid to talk throughout the entire match, even if it means shouting to make themselves heard.
Being heard is important, being seen is equally so. A goalkeeper should try their hardest to inspire fear in the opposing team. For this, they have to be totally engaged, especially when jumping to block the ball (without going overboard like Schumacher). You don't have to be tall to get things done! Above all, you need to have the drive and, most importantly, good reflexes. Being able to read the game helps the goalie get in a good position to make a diving save, without risking injury.
The goalkeeper is essential to the game, they shouldn't be passive, stuck to the line, waiting on the opposing team's defence. They should participate in the game with their movements. Rather than staying on the line, they have to adjust their position based on what is happening on the field. This will help them intervene and better anticipate their opponents' shots and teammates' errors.