I find it's easy to get 120apm with the 'Z' key

4sdddddddddd, 4szzzzzzzzz is all I do all game. I find I have more apm when I play as zerg vs the other races, just because there is so many more actions per thought.

Build units: well zerg has the swarm, so you have to build more.

Move army: well zerg units move faster so you have to spam click the screen to be precise.