How to be stronger in the air?

Basically, I'm a goalkeeper, and not a big one, so i don't have much presence in the box. Are there ways of competing for a ball in the air and knocking everyone else out of the way. I thought maybe one solution was to jump up, go through the attacker and into the ball. There must a technique because when pro goalkeepers rush out and collide with defenders and attackers, they always seem to catch it, whilst everyone else goes flying, it's rare to see the goalkeeper knocked over.