....... Basically you're problem seems to be it not being a COD or a Halo clone.
Or controlling like any other console FPS for that matter....
I'm going to assume you've never fired a weapon in real life.
Anyway, I don't have much of a problem, be it aiming or moving, but I'm also playing the game at the default setting for speed, which helps a lot.
Aiming is essential, if you're having a huge problem with it, hten you're too close. You have to understand, Iron Sights are only used in mid to long range, and most games get iron sights terribly wrong (like CoD4, for instance).
What I recommend is turning off the cross hair. I did, and it really really helps me, especially with the immersion, and will help you better judge when to use your iron sights, and when to fire from the hip.
I am only using 'iron sights' at mid/long range, shooting enemies across the street, in balconies etc, or when they're in cover and I want to shoot their helmets off.
I'm currently at the part in level 3 where you have to defend against waves of enemies, I just finished the cable car wave no problem, but now there's one where two heavy's approach you from either side. It is absolutely BS how hard they are to kill, you have to do the 'make them turn around and shoot their tanks' rigmarole like 8-10 times to kill them all while being shoot at by their escort of other Helghast, and their two of them.