Perfect your game in stacks starting 30BBs and less. That means you gotta learn the differences of playing in such stack sizes as 1-15bbs, 16-22BBs, 23-35BBs (rough estimation). Each of them has its own nuances. Ability to play these stack sizes (and against each of these stack sizes) is what is the skill in MTT, because in tournaments the majority of time you gonna be playing in stacks under 30-35BBs, and it's the stack sizes of important pay jumps and final tables as well.