Broken
There are two good books written by TImothy Zahn, Allegiance and Choice of One. Both are books set between the IV and V movies and they go in depth about a group of stormtroopers and their lives. It explains a lot more about their training and actually how good they are and how their armor isn't as bad as you would think. Now this isn't canon anymore, canon would have you believe they were wearing plastic pieces of armor that can't stop a rock which isn't true.
Also as its been pointed out numerous times, clone troopers were cloned from Jango Fett, who was picked because of how deadly he was. A comic has him killing nearly a dozen jedi with his bare hands. Towards the end of episode III timeline, in a off series by Karen Traviss about Clone Commandos, it goes into some detail about how towards the end of the war Palpatine mass produced clones by the tens of thousands if not more. They could be grown in less than a year but they had flash training, not real physical training, and it made them sub-par from their clone trooper brethren. If you take all that into account that is "Not Canon" you can actually get a decent explanation about lack of training and why maybe they were just bad shots at times.
Or you look at it because the stormtroopers were tasked to do that for several reasons, finding the rebel base, capturing Luke and so on and so forth. Lots of explanations, its up to you to choose which one you like the best!
Also as its been pointed out numerous times, clone troopers were cloned from Jango Fett, who was picked because of how deadly he was. A comic has him killing nearly a dozen jedi with his bare hands. Towards the end of episode III timeline, in a off series by Karen Traviss about Clone Commandos, it goes into some detail about how towards the end of the war Palpatine mass produced clones by the tens of thousands if not more. They could be grown in less than a year but they had flash training, not real physical training, and it made them sub-par from their clone trooper brethren. If you take all that into account that is "Not Canon" you can actually get a decent explanation about lack of training and why maybe they were just bad shots at times.
Or you look at it because the stormtroopers were tasked to do that for several reasons, finding the rebel base, capturing Luke and so on and so forth. Lots of explanations, its up to you to choose which one you like the best!