OK it's not ALL about aim and movement. It's also exactly what you said about anticipating to the enemy's decisions.
For example in factory your enemy takes the upper HP spawn (or you), you should instantly go for the lower spawn too in the tunnel thingy.
Using the barrells you can pot them and simply deal great amount of damage so you are 1 step ahead of your enemy.
But let's be for real, if you can move and aim really good then you don't even need that much gunz expierence, just a decent set of brains.